How room thermostats, programmers, thermostatic radiator valves and smart controls work together, how to set them for comfort and lower bills, and common mistakes.
Good heating controls let you heat the rooms you use, when you use them, to the temperature you want, without wasting energy. Most homes have a combination of a programmer or timer, a room thermostat and thermostatic radiator valves (TRVs). Understanding how they work together is the key to using them well.
The main controls
Programmer or timer
Sets when the heating (and hot water, if you have a cylinder) comes on and goes off. Set it to match your routine: for example, on shortly before you get up and before you come home. Some boilers take a while to warm the house, so experiment with start times.
Room thermostat
Sets how warm the house gets. It switches the boiler on when the temperature where the thermostat is located falls below the setting, and off when it is reached. Turning it up does not heat the house faster; it only makes it hotter in the end. Many people are comfortable between about 18°C and 21°C. Each degree lower generally reduces heating costs.
Place the thermostat in a room you use often, away from radiators, sunlight, draughts and kitchens. It should not be in a room with a TRV that could shut off the radiator before the thermostat is satisfied.
Thermostatic radiator valves (TRVs)
Fitted to individual radiators, they control how warm each room gets by reducing the flow of hot water when the room reaches its setting. The numbers (often * and 1 to 5) correspond to approximate temperatures; check the manufacturer's guide. Set lower numbers in rooms you use less, such as bedrooms or spare rooms. Do not cover TRVs with curtains or furniture, as they sense the air around them.
Cylinder thermostat
If you have a hot water cylinder, a thermostat on it controls the stored water temperature. To control the risk of Legionella bacteria, stored hot water is generally recommended to be kept at 60°C or above.
Smart controls
Smart thermostats let you control heating from your phone, set schedules easily and, in some systems, control individual rooms using smart TRVs. Features such as geofencing (turning heating down when everyone is out) can help. They save energy only if they lead you to heat less; a smart thermostat set to 23°C will still be expensive.
Boiler flow temperature
Condensing boilers work most efficiently when the water returning to the boiler is cool enough for the boiler to condense. Many combi boilers are set to send water to radiators at a high flow temperature. Lowering it (for example to around 60°C) can improve efficiency while keeping homes warm, though rooms may take longer to heat up. Check your boiler manual or ask a heating engineer. If you have a hot water cylinder, do not lower the hot water temperature below the safe level.
Heat pumps
Heat pumps work best running at low temperatures for longer periods, so the settings that suit a gas boiler, such as short bursts of high heat, are not ideal. Follow your installer's advice.
Common mistakes
- Turning the thermostat up high to "heat faster".
- Putting the thermostat next to a heat source or in a cold hallway.
- Leaving TRVs on maximum everywhere.
- Heating empty rooms with doors open.
- Switching the heating off completely in very cold weather, which can increase condensation and the risk of frozen pipes.
Step by step: set up your controls
- Set the programmer to your routine.
- Set the room thermostat to the lowest comfortable temperature, then try lowering it by 1°C.
- Set TRVs lower in rooms you use less.
- Check your boiler's flow temperature with the manual.
- Review after a week and adjust.
Sources and further reading
Facts checked on 20 October 2026. Spotted an error? Tell us and we will correct it.