Managing your central heating

NB. This page is about central heating systems. If you have electric heating with night storage radiators, we recommend you look at the CSE advice page here.

Space heating accounts for 2/3 of our home energy use. If you want to reduce your energy use this is an area you can't ignore. You can save energy with your heating system by

(1) If you have a condensing boiler or a heat pump Heat pumps and condensing boilers are more efficient when supplying heat at lower temperatures. This means there is a trade-off between heating efficiency and heating for less time or less space. To get the most efficiency you need to lower the temperature in the radiator circuit. However, this reduces the heat generated from the radiators which means it takes longer for rooms to heat up from cold. Also, if you leave some rooms without heating, the adjacent rooms leak heat into them and their radiators need to work harder; if the radiator circuit temperature is reduced they may not cope.

The best approach for your case depends on how quickly your home uses heat. If it loses heat quickly, then heating for less time and space is probably best. However if it keeps its heat reasonable well, then opt for the low radiator temperature approach. Rather than turn the heating off altogether, with a programmable thermostat you can turn it down a few degrees. This saves some energy but ensures that the house does not get so cold that it takes a long time to warm up. If the house is well insulated it will not get too cold anyway, except in the coldest weather.


What heating controls should I have?

As a minimum you should have

  • a programmer (for controlling the times when you want heating )
  • a wall thermostat (to set the temperature)
  • thermostatic valves on the radiators for per-room control
  • a thermostat on the boiler controlling the temperature for the water that goes around the radiators
  • a thermostat on the hot water cylinder (if you have one) to control how hot it gets

All homes now being built also have at least two zones, each with a separate wall thermostat. Large homes should have a timer for each zone too. Then, for example you could have the bedrooms in a separate zone which is heated at different times.

You should have thermostatic radiator valves (TRVs) on all radiators except by the thermostat. If there is a TRV there as well, set it to max, otherwise the thermostat may never get warm enough to turn the boiler off.

Also, some boilers need at least one radiator without a TRV or a bypass in the system to ensure a minimum flow of water through the boiler. In some boilers the bypass is within the boiler unit.

If you have a hot water cylinder

If you have a hot water cylinder this should have a thermostat too so that the boiler can know when the hot water is hot enough. If you don't then the boiler can only tell when the cylinder is hot by sending some hot water round and seeing how much cooler it is when it comes back. This means it has to turn on just to check. Also, if the pipes between the boiler and the hot water tank are not well lagged the water will cool regardless of the temperature of the cylinder so the boiler will always think the tank is not hot enough.

How do you know if you have a thermostat? The thermostat is usually mounted on the side of the tank and it has a dial to set the temperature. (Sometimes the thermostat is just a sensor and the setting is controlled by the heating programmer).

Thermostats are not expensive but fitting them can be complicated because they have to connect to the boiler. It may not be worth fitting a cylinder thermostat as a separate job but if you are changing your boiler, your tank or adding other controls then it would be a good idea to fit a thermostat at the same time.

If you have an immersion heater this will have its own thermostat inside the cylinder. Changing the setting usually involves taking the front off and tweaking with a screwdriver. This should only be done by a qualified electrician.

What are heating zones and how many should I have?

Heating zones allow you to set different heating patterns in different parts of the house. Each zone has its own wall thermostat and timer. For example with 2 zones, for bedrooms and living room, you can heat the bedrooms first thing and again before bedtime, while the living rooms warm up later in the morning and earlier in the evening. If you only have one thermostat, say this is in the living area, then if heat is not required in the living area the boiler will not turn on and you will not get heat in the bedrooms either. Having zones means the boiler turns on when any of the zones want heat.

Zoned heating can be installed by organising the plumbing with a separate radiator circuit for each zone or electronically using radiator valve actuators which are turned on and off from a controller. To save wiring this can be by wireless control and the actuators can be battery powered though the batteries only last a couple of years.

As for how many you should have, it depends on how big your house is, and what are your usage patterns. For example, you could have one zone for areas you use during the day (workroom, office?), separate from areas you use in the evening.

You can also have programmable controls on each radiator, which gives you a zone per room, except that the boiler will still turn on and off dependent on the wall thermostat.

I donít have a wall thermostat - should I get one?

If you don't have a wall thermostat you must be relying on the boiler thermostat; this measures the return temperature of the water as it comes back from the radiators. If you have fitted thermostatic radiator valves and adjusted them to your needs, then when the rooms are warm enough the circulating water bypasses the radiators and returns to the boiler almost as hot as it started, though it will also be losing heat from the pipes in the circuit between the radiators and this loss can be substantial - in most cases these pipes aren't lagged. If the heat loss is small the boiler will notice this and shut off. However, even then it needs to keep checking, so it periodically sends water round the pipes to see if heating is needed. If you have a room thermostat, this will turn the boiler off completely and will make at least some savings.

If you donít have thermostatic radiator valves and your rooms are warmer than you need then a room thermostat will help a lot.

Is it easy to add a timer or a thermostat to my heating system?

Maybe - it depends on whether or not you already have a boiler interlock which allows the timer to turn the boiler off when it isnít needed. If you havenít got one you will need to have one fitted.

Is it worth having radiator thermostats?

Thermostatic Radiator Valves (TRVs) allow you to keep some parts of your house warmer than others. You can adjust them through the day according to need, or you can leave them on one setting most of the time. For example if you have a spare room you donít use you can turn the thermostat right down except when you have a guest coming to stay. You might keep your bedrooms cooler than your living room, or turn them off during the day and only turn them on shortly before bedtime. You will need to keep doors closed as well to reduce heat leaking in from other parts of the house. There is a tradeoff between reducing heating in some parts of the house and keeping the radiator temperature low to improve efficiency (see also How should I set my radiator thermostats?.

How much you save with TRVs depends on how much of your house you can reduce the heating in. A TRV can cost as little as £10 but you do need one per radiator and unless you plan to fit them yourself you will need to pay the plumber too. They will need to drain the system to do this.

Can I get a thermostat that sets different temperatures for different times of the day and week?

Many programmable thermostats can do this. You can set different temperatures for different time windows during the day. For example you could have different settings for getting up in the morning, early evening and late evening.

Can I get a grant for heating controls?

You may be able to get a grant towards heating controls up to the current recommended standard (which is a programmable timer and thermostat and TRVs). See our Finance page.

Where to put things

What is the best place for my radiators?

You want air to be able to circulate in front of your radiators and into the room

  • If you have a radiator under a window, make sure there is a shelf above that deflects the warm air away from the window surface. Also if you have curtains do not allow them to hang in front of the radiator - you want to heat in front of the curtains not behind them.
  • If they are on an outside wall you should have a foil reflector panel behind them or you will lose lots of heat through the wall. This is especially the case if you have solid walls.
  • If the radiators are behind furniture the warm air may not circulate freely. This could be nice to warm your feet under your desk but warming the back of the sofa is not very helpful
  • Warm air rises but you notice the cold most at ankle level so ideally you want the heat to be delivered low down - you can even get radiators that fit into your skirting board. However, if your house is draught free and has normal ceiling height you should find that any shape, tall or wide (or even T-rex if that takes your fancy), will do as the air circulates around to warm up the whole room eventually.

How can I extend the window sill over a radiator?

If you have a radiator under a window the ideal is for the curtain to sit just above the window sill and the window sill to extend over the radiator. This deflects warm air from the radiator into the room and not up the window behind the curtain.

If you need to extend your window sill, an easy way is to fix a piece of 9mm plywood on top of the existing sill, to the extra width you require. Then add a strip of timber underneath the overhanging section to make up the full thickness and create a robust front edge. There is skill involved in hiding the joints but at least the top face has no joints, and that is the bit on full show.

What is the best place for my wall thermostat?

If there is one room that you spend most time in and keep warm, then that is the best room for the thermostat. Alternatively it should be in a room which is central in the house. If you have a wireless table top thermostat you can move it around until you find the best place, or keep it with you all the time.

In any case it is best on an internal wall, and away from direct heat sources including radiators and also electrical equipment such as TVs or computer monitors. It is usual to put thermostats at about head level. If you put them lower then you should set the temperature a little lower than you would have done because the air is usually cooler at lower levels (especially in draughty houses).

You should not have a TRV on any radiators in the room with the wall thermostat. If you do then it is possible for the TRV to shut down the radiator before the thermostat shuts off the boiler, so the room never gets hot enough to trip the wall thermostat and you will find the boiler runs all the time whether you need heat or not.


How should I set my wall thermostat?

Most people set their wall thermostat somewhere between 17C and 21C. Some people don't like to be too warm but some feel the cold very easily, especially in hands and feet. If you have vulnerable people in your house - such as someone elderly who is not very mobile and might fall and be unable to get up - then you should set the thermostat to at least 18C.

Reducing your thermostat setting is one of the simplest ways to save energy. Dropping it one degree can save up to 5% on your heating costs. However, it can take a little time to get used to a lower temperature. Make sure you are warmly dressed and try reducing the thermostat setting a little bit - at most one degree. If that feels cold, persevere for a week or two. If you still feel cold turn it up again. If you feel quite comfortable at the lower setting, try turning it down a little more.

Some people are prone to cold hands and feet even when the rest of their body is warm. (In extreme cases this is called Raynaud's Syndrome.) Fingerless gloves or wrist warmers and warm socks can help.

How should I set my radiator thermostats?

You can use radiator thermostats to reduce the temperature in individual rooms. This saves energy because the lower temperature the lower the heat loss. However, if you have a condensing boiler or a heat pump there is a bit of a tradeoff to manage. This is because any warm room next to the cooler room will leak heat into it and so the radiators in the warm room have to work a bit harder and they may need to be a bit hotter - which will make your boiler less efficient. If you find the radiator in the warm room is not adequate, it is often better to turn up the heating in the cold room rather than turning up the boiler temperature which makes the whole house heating less efficient.

The TRV works by reducing flow in the radiator - or shutting it off altogether - when the room is warm enough. However, setting your radiator thermostats can be tricky because any change takes a while to have an effect and you don't get a click when the valve opens or closes. There are a few easy cases:

  • If there is a TRV on the radiator close to your wall thermostat, set it wide open. If this valve closes before the wall thermostat turns off then your central heating will never shut down.
  • If you don't want any heat in a room turn the thermostat right down, or to the frost setting if there is one.

For other rooms you will need to experiment. Make sure the heating is on first. Then go into each room and see if it is too warm or too cool: tweak the radiator valves up or down accordingly. If you have turned the heating up, check in a few minutes to see if the pipes are warm showing that there is hot water coming in. If not, tweak some more. If you have turned the heating down then the pipes will cool but this will take some time. Check the room temperature again after half an hour (making sure the heating is still on) and tweak some more as necessary.

For rooms I rarely use, should I turn the heating off completely or keep them a bit warm?

Even if you turn the radiators off and close the door some heat will leak through from the rest of the house and you will find this is enough to keep the pipes in the room from freezing. However it may feel a little damp after a while, in which case you should ventilate the room sometimes. Also there is the tradeoff between keeping rooms cool and reducing the boiler temperature - see How should I set my radiator thermostats?.

When I am away in the winter, how should I set my heating to stop the pipes freezing?

7 C is probably warm enough but you would need this on all the time, through the night as well as during the day. (See also frost protection and holiday mode).

How should I set my heating if I go away, but my pets are still at home?

Cats and dogs are usually good at finding a warm place; with adequate bedding they should be OK as long as the house is always above freezing. More exotic pets like birds may need a warmer environment, so the room they're caged in should be kept at the right temperature. A vet should be able to advise you on the best temperature for any animal.

At what temperature should I set the boiler?

Combi boilers have two temperature settings: one for the radiators and one for hot water. Other boilers may have two (one for radiators and one for heating the hot water cylinder) or just one. For condensing boilers the lower the better as this makes the boiler more efficient. However, it does need to be hot enough.

The radiator temperature setting needs to be warmer than the room thermostat - and the hotter it is the faster radiators work to warm the rooms. It needs to be hot enough that the radiators can keep the rooms warm on the coldest day. Also the hotter the radiators the faster rooms warm up. However, if the radiators are very hot people can burn themselves by touching them and also condensing boilers lose efficiency. Condensing boilers are very often balanced to give you a 20C temperature drop from 70C down to 50C. That means the boiler thermostat is set to 70C and the water returning from the radiators is 50C in cold weather However, dropping down to 55/35 will give you better performance - for more advice we recommend the Heating Hub.

If you have a non-condensing boiler, it is normally balanced to run at 80C with a drop of 10C through the radiators, so the return temperature is 70C. This is hot enough to avoid condensation, which would cause lots of problems.

If you only have one setting you need to set the thermostat to be either the radiator temperature or the temperature for the hot water heating circuit whichever is the higher. The hot water heating circuit needs to run at a higher temperature than the hot water cylinder thermostat (see below), otherwise the cylinder will never get hot enough.

What temperature should I set the hot water cylinder thermostat?

The temperature for your hot water needs to be hotter than you need it for showers and baths, hot enough that you don't run out of hot water and hot enough for safety.

For showers 40C should be fine. For baths you might need it a bit hotter because you have to heat the bath itself and also it cools over time.

However, if the cylinder is only just hot enough then you are limited by the size of the cylinder. For example if you need 120 litres for showers and you only have a 100 litre cylinder, and heated to 40C then you would run out. But if you heat the cylinder a bit more - say 46C then you can mix cold in to get the right shower temperature and not run out.

The main safety concern is that bacteria (such as legionella) could grow in your hot water cylinder if the water is not hot enough. The rule of thumb is that 60C will kill anything, and for simplicity you can run your cylinder at this temperature. However this does increase the heat loss from your cylinder and it also can lead to burning your hands under the tap. In fact it is not necessary to heat the cylinder to 60C all the time - just an hour a week or every 2 weeks should be fine.

See also this great video from Heat Geek: What temperature should your hot water be?

I have a solar panel for hot water - what difference does this make?

To get the most energy from your solar panel you need to time the water heating so that it tops up the heat in the water tank only when necessary and only as much as necessary. You should time this to heat up the water before you use it, or at least after the sun has done as much as it can. For example, if you mainly use hot water in the morning 7-9am then you could top up the tank in the morning around 6am so there is enough when you need it. During the day the sun will give you free heat and if this is not enough the boiler will supply the difference the next morning.

You can allow your solar panel to heat your water hotter (thus storing more energy) if you have a thermostatic mixer valve to prevent scalding - the mixer valve will mix in enough cold to make the water from the taps safe.


I am cold and the radiator in here is cold Ė what should I do?

Check the boiler is on. If it is not, check the programmer timings and the thermostat Ė adjust this upwards if necessary.

Otherwise, if the radiator is partially warm, check for air in the system. If the radiator has a TRV try turning it up. If that doesnít help it may be stuck: see My radiator has a TRV but it is always on (or always off)

I am warm so why is the boiler still on?

Is it heating the radiators or only the hot water? If it is running heat through the radiators, check the thermostat and consider turning it down.

My radiator has a TRV but it is always on (or always off)

Radiator valves can sometimes stick. Try turning it right down, then up, then back to where it was. If it still stuck you can try removing the head of the valve and fiddling with the pin to free it up or tapping it as described in this video. If it is totally stuck then you may need a new valve which means draining the system. If you have other valves of a similar type and age then they will probably fail soon too and you should replace them all at once, because draining the system is expensive you don't want to do it more often than you have to.

How can I warm the house up more quickly?

Adjusting the wall thermostat wonít help Ė this is either off or on. You can adjust the boiler to increase the temperature of the water circulating round the radiators. However, if this is very hot then children or vulnerable adults could scald themselves on the radiators. Or you can fit a control with a load compensator

It takes a lot of energy to warm up this house Ė wonít I save by leaving the heat on all the time?

For most people it is better to let the house go cold when you donít need the warmth. When the house is warm it loses more heat than when it is cold so if it is warmer than it needs to be it is losing more heat too. However, if your heating system takes a long time to heat the house then you might like to use a delayed start system which automatically adjusts the start up time depending on the temperature.

However, for condensing boilers and heat pumps there is a bit of tradeoff between getting good efficiency and heating up quickly. To heat quickly the radiators need to get hot which reduces efficiency. This is why households with a heat pump are often advised not to let the home get too cold so that it takes a long time to heat up again. You can do this with a programmable thermostat by setting the temperature for overnight to be a few degrees colder than during the day. Also if you are out during the day you can set the thermostat lower by a few degrees at that time.

This means there is two alternative strategies:

  • Minimise the radiator temperature, for example using weather compensation, but do not let the rooms get too cold
  • Run the radiators hot so that the home heats quickly and only heat the house when you are in it.

If your home gets cold quickly when the heating goes off, then it is probably better to use the second approach. Also if your home loses heat quickly you would be better to improve insulation before getting a heat pump.

Finally, if your house is taking a long time to heat up it could be because you have high heat loss through draughts and poor insulation. Stopping up draughts and improving your insulation will reduce this. However, your house may take a long time to heat simply because it stores heat in the walls and floors - this can be a good thing as it will also stay cooler for longer in summer.

My radiators arenít warming up evenly. What is wrong?

If the radiator is cold at the top it probably has air in it. You need a radiator bleeding key: with this you open a valve at the top to let the air out. When fluid starts coming out you close the valve. Itís a good idea to have a tissue or a cloth to mop up.

If the radiator is cold in patches then it may be blocked up with sludge or scale. It needs to be flushed through with descaler to clean it out. You will need a plumber for this unless you are a confident DIYer.

NB. Every time the radiator system is refilled a chemical inhibitor should be added to prevent scale.

My boiler is very noisy - what is wrong?

Your boiler should run quietly. If it is noisy there could be something wrong with the pumping system. One possibility is if you have valves on all your radiators turned off and there is nowhere for the water to flow. You should either have an automatic bypass, which cuts in when nothing needs heat, or you need to keep one radiator always open so that there is somewhere for the water to flow. Many modern boilers have an internal interlock but older systems do not. In that case you should not put TRVs on all your radiators - you should leave one fixed open. (In any case you should not put a TRV on the radiator in the same room as the room thermostat.)

How long should a condensing boiler last?

Boilers should last at least 10-15 years - longer if maintained well. You can get guarantees for 5, 7 or even 10 years from reputable manufacturers.

Boiler lifetime is restricted largely by the availability of parts: manufacturers may stop supplying parts 10 years after the boiler model is taken off the market. This means it is a good idea when you buy to get a new model which is early in its sales cycle so that you will continue to be able to get new parts for longer. When parts are no longer available you should consider replacing your boiler before it actually stops working to avoid the difficulty of getting a new one in an emergency.

My condensing boiler keeps freezing up in cold weather

Here is some good advice from Which. Basically, the tips are:

  • Install the drain inside if possible, otherwise have as short a length of outside pipe as you can
  • The outside piping should be at least 32mm wide and it should be lagged and as steep as possible.
  • Ideally, get a boiler with a siphon system so the condensate comes out in pulses, rather than dribbling out slowly


What is a condensing boiler?

A condensing boiler is more efficient than an old fashioned boiler, at least it is when it is adjusted correctly. When natural gas burns it generates a lot of steam as well as carbon dioxide and if the steam condenses it forms hot water which can corrode metal quite quickly. Old fashioned boilers are designed to avoid this problem by running sufficiently hot that the steam does not condense. However, condensing boilers have protection against corrosion so that it is OK for the steam to condense. In fact, it is a good thing if it does because this gets more heat out. In a condensing boiler, the hot gases are used to preheat the water coming back into the boiler, cooling them down so the steam condenses and gets the maximum heat out. This only works, though, if the water coming back from the radiator circuit is at 55C or cooler. Hence condensing boilers are generally configured with a flow temperature of 65-70C and a return of 45-50C. For best performance the return should be no more than 45C, so that condensation is reasonably complete.

What is delayed start/optimum start?

Optimum start or delayed start is a feature for the programmer. Normally you set the program times for when you want the heating to come on and turn off. With this feature you set the program times for when you want to be warm and the system decides when it needs to turn on. When the house is cold it turns on early but in mild weather it will switch the boiler on later because it doesnít take very long to warm the house up.

What is a load compensator/ weather compensator?

A load compensator adjusts the radiator circulating temperature to be hotter when the house is cold. The weather compensator does the same depending on the weather (measured using an outside thermometer). This means you can run the radiators cooler when less heating is needed. This is a good thing because condensing boilers are more efficient at lower temperatures: ideally the water returning to the boiler should be no warmer than 55C. A modulating boiler has similar functionality. It senses the return temperature and adjusts the burn rate to get this right.

What is the set back temperature?

Some programmable thermostats have a set back temperature which is like a default or standby temperature - when the heating isnít Ďoní, for example overnight, it will still maintain the house at this temperature.

What is a boiler interlock?

This is the system which allows your thermostat and programmer to tell the boiler when to turn on and off.

What does balancing the system mean?

Balancing the system is a matter of optimising the radiator valves and the boiler pump rate to get an optimum temperature drop through the whole circuit and in each radiator. If you don't balance the system then the upstairs radiators tend to get all the heat and the last radiators in the circuit take a long time to warm up. Also, the radiator return temperature needs to be appropriate for your boiler type - low enough to get good condensation in a condensing boiler, or high enough to avoid condensation in an older boiler.

What is frost protection mode?

This is a minimum temperature which always applies, regardless of the other settings. This should be just enough to keep your pipes from freezing - around 5-7 C

What is holiday mode?

Some programmers allow you to tell them when you are going on holiday and, more importantly, how long you will be away. When in holiday mode your programmer will keep track of the days and reset to normal before you return so you can come back to a warm house.

What are smart heating controls?

Smart heating controls can mean a lot of different things. For example, load compensation is a smart control, especially if it 'learns' how long it takes your house to heat rather than asking you to select a temperature curve. Smart controls can also:

  • Give you remote control through your smart phone (e.g. from SMS central heating or heat miser)
  • Turn the radiators down 1 or 2 degrees when there is no-one in a room, or no-one at home
  • Prioritise flow through radiators where there is heat demand and adjust the radiator flow temperature when necessary
  • Turn the radiators off when the front door is open or windows are open
  • Set the programmer for you by learning from you what your requirements are (you have to tell it if you are too hot or too cold) such as Nest.

There is a european standard for smart controls (EN 15232) which describes the services which can be provided and estimates the savings achievable in different situations. For a residential property with full automation the savings (over the reference case which is for a home with a condensing boiler, programmable thermostat with weather compensation and TRVs) are around 20%. There is a paper about this standard here.

Geo is a local company that deals with smart controls.

Why would I want a presence sensor?

A presence sensor connected to your radiator valves can turn them down by 1 or 2 degrees when you arenít in the room - enough to save some energy but not enough that it canít warm up quickly when needed. If your house has a high thermal capacity it may take too long to warm up for this to be useful.

% What is chemical inhibitor?

Inhibitor fluid is a chemical additive for the water that goes around your radiators to stop corrosion and scale. You should add inhibitor every time you have to drain and refill the system. Also it is a good idea to add inhibitor every 5 years or so because it gets 'used up'.


How can I find a good heating engineer?

The Institute of Domestic Heating and Environmental Engineers - has a register of members you can look up by postcode.

In Cambridge, we recommend Green Heat

The Chartered Institute of Plumbing and Heating Engineering maintains a register of competent professionals. You can find your nearest professionals by postcode.

If you have gas central heating then you must use a Gas Safe registered engineer.

Where else can I get information?

We recommend:

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