Do thermostats work and are they effective?#

If you can see clear evidence from the data plots that your thermostats and thermostatic radiator valves (TRVs) are working, then you can skip this page.

Finding the thermostat

Not all thermostats come as a box with a dial on it.

  • You could have a programmable room thermostat that combines the timeswitch and thermostat in one box.

  • The temperature reading might be taken somewhere else, using a remote sensor that doesn’t have an user controls on it. They’re usually just a plain white box.

  • A radiator could have a thermostatic radiator valve (TRV) that controls whether hot water can flow into the radiator.

  • With smart TRVs, changing one TRV’s setting could change all the TRVs in the room.

Non-working thermostats are common:

  • Wired thermostats might be from a previous system. Some venues purposely leave a decoy stat on the wall to give users something to try. Heating system installers often leave parts of previous systems in place unless asked specifically to remove them.

  • Wireless thermostats could have flat batteries, be out of radio reach of the boiler, or be suffering from radio interference.

  • Thermostatic radiator valves (TRVs) often stick or are missing the heads to control them.

If you have a building or heating zone with one room thermostat and thermostatic radiator valves otherwise, it probably turns the boiler or zone off when the right temperature is reached. If anyone turns down a thermostat that turns the boiler off, people in the other spaces won’t be able to understand why the heating isn’t coming on. If that’s a problem, it suggests you need a change in the control system design.

Here are some ways of testing your thermostat and what it does.

  • To test what a room thermostat does and whether it is working, station someone at the boiler, make sure the timeswitch is calling for heat, and see if you can get the boiler to turn on and off by using the dial.

  • If you can’t get the boiler to turn on and off, and you have smart TRVs in the room, it’s possible the thermostat is controlling them and using it will stop and start the flow of hot water into the radiators. Otherwise, look for a motorised valve controlling the flow of hot water to the zone the thermostat is in. Changing the thermostat setting might change the valve position and slowly make a difference to the temperature of the pipework on the two sides of the valve.

  • To test whether a thermostatic radiator valve is working, turn the dial while there is hot water supplied to the circuit and see if the radiator heats or cools. You might be able to tell from the noise whether water is flowing into the radiator.

A thermostat could technically be working, but be ineffective because the temperature they report bears no relationship to what users feel. This is usually because it is badly placed - for instance, attached to a very cold stone wall that overwhelms its sense of the air temperature, in a corner with low airflow, above a heat source, or in the sun. This is especially likely for wired thermostats, since electricians prefer convenient locations. Thermostats need the same kind of locations as thermal monitors, so you can use the description we give for those.

If there is a thermostatic radiator valve so badly positioned the readings are useless, it is possible to use either smart TRVs or sometimes a unit on the wall that has a wire running to the valve.