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Thermostatic radiator control valves (TRVs)

TRVs are not expensive and can be fitted by DIYers who are comfortable with plumbing. Generally, one radiator should be left without a TRV and left permanently switched on, unless the boiler is fitted with a flow meter to detect when all the radiator valves are closed. This special radiator may be a bathroom towel rail (where the heat is always likely to be useful), or in the same room as the room thermostat. It is not a good idea to have a TRV on the radiator in the same room as the main thermostat, as if it turns the radiator off at a lower temperature, it can mislead the main thermostat into thinking that the house is cooler than it really is.

Thermostatic controls on the hot water system

This section does not apply to combination (Combi) boilers, but only to systems with a separate hot water tank. Firstly, it is most important that the hot water can be controlled by the programmer separately from the central heating. Some older systems only allow the heating to run when the hot water is on; this can be quite wasteful of fuel. Secondly, there should be a thermostat on the hot water tank - this is usually strapped to the outside fairly near the bottom. This controls the water temperature - it should not normally need to be set higher than 60°.

The room thermostat and the hot water thermostat should be wired up to the boiler in what is known as an "interlock". This means that if both the house and hot water are at temperature, the boiler will be switched off. If this does not happen, when the water temperature inside the boiler itself falls, an internal thermostat will cause the boiler to fire to heat up this water - a process known as "dry cycling". All the energy used in this cycle is wasted as it is not used for any useful purpose.

       
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