Demystifying heating controls

Many people are baffled about how to get the best out of their heating system, both in terms of achieving a comfortable temperature and reducing gas consumption. We are not experts - just amateurs trying to understand and pass on hints in non-expert language. There's plenty of excellent expert advice around, notably the Energy Savings Trust but this page attempts to provide a simple summary of the basic elements of domestic space heating based on a gas boiler feeding hot water to radiators.

NB There are many other types of heating system not included

Components of a domestic heating system
There's a dazzling range of products and terms-  condensing boilers, non condensing boilers, timers, programmers, thermostats, thermostatic radiator valves,TRVs, wall thermostats, central heating controls, programmable room thermostats, room thermostats, time switches, full programmers, mechanical thermostats, non programmable thermostats, programmable thermostats, etc.

But whatever individual gadgets are fitted, most homes seem to have the following broad types of equipment with knobs, dials and digital displays. These components all have control settings that affect how well the heating system operates.

There is some confusion about condensing and non condensing boilers. Basically, condensing boilers are much more efficient in terms of gas consumption so it is probably worth considering an upgrade if you have an old non condensing boiler. There is also some confusion about combi boilers. These are boilers that supply domestic hot water on demand rather than by storing it in a tank. They can be condensing or non condensing.

Gas boilers typically include controls to set the water temperature and water pressure.

Boiler timer /programmer
Most gas boiler heating system include a device (installed at the same time as the boiler) to set the time periods when the boiler will operate.

Older mechanical timers can be replaced with an electronic programmer to gain greater flexibility for programming the times that the boiler will operate. However, some people find electronic programmers baffling in their complexity and revert to just switch the heating on and off manually.
Don't despair - try to get to grips with the programmer - with a good pair of glasses, a strong light and a lot of determination, it should be possible to get the timings tuned to your requirements.
Aim for timings that do not heat the home for longer than necessary, i.e. half an hour before you get up to half an hour before you leave for work and half an hour before you arrive home to half an hour before you go to bed.
It may be useful to adjust timings in very cold periods (see notes on room thermostats)

Room thermostat
The simplest form of room thermostat is linked to the boiler and turns it on and off during the timer periods according to the temperature of the air around the thermostat, i.e. it switches on the the boiler to heat and circulate water around the radiators until the air around the thermostat reaches the temperature set. It then turns the heating off until the temperature drops.

Programmable room thermostats combine time and temperature controls so that different temperatures can be set for different times of the day and night. A mechanical timer / room thermostat is an alternative (possibly simpler) option to digital controls.

Radiator thermostats
Older radiators may just have valves to limit water circulation. Unless they are very well maintained, they are likely to be stuck and not an effective way of controlling the temperature.

Thermostatic radiator valves (TRVs) sense the air temperature around them and regulate the flow of water through the radiator they are fitted to. They do not control the boiler, but setting them to a lower level means that the boiler will use less energy to provide sufficient hot water.
Install  and utilise TRVs to set different temperatures in individual rooms, i.e. turn off radiators and shut the door on unused rooms and set lower temperatures in bedrooms than in living rooms.
TRVs sense the air temperature around them and control the flow rate depending on what level they're set at. Having a cover over the radiator means that heat will be trapped between the radiator and the cover so the TRV is likely to react as if the room temperature is higher than it actually is and switch off before the room is at the required temperature

Information sources
Energy Saving Trust -
Boiler manufacturers websites have useful guidance e.g.