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Thermostatic Radiator Valves

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TRVs fit on the radiator in place of the existing valve, inside the valve is a wax capsule which expands when heated and stops the flow of water to the radiator. As the wax cools it contracts and lets the water from the boiler flow into the radiator.

You should only fit TRV's to all radiators providing there is a bypass fitted on the system (or leave one or two with lock shield valves) but even then this is not advisable as it could increase your fuel bills and increases wear and tear on your boiler. This is because once all the rooms are up to temperature all the TRV's will be closed, but your boiler will still be producing heat at about 78 deg °C.

The pump will still be pushing the heated water around the bypass circuit, even though the house is warm enough. This will cause the boiler to cycle unnecessarily. It is a legal requirement for all new central heating systems to have a room thermostat fitted. For older systems with no room stat it is advisable under the new energy efficiency regulations to have one fitted.  When the room stat is satisfied it will shut the pump & boiler off (providing another circuit is not calling).

When choosing a TRV check that they are full flow valves as some have a higher restriction.  A valve with only an 8mm diameter hole for the water to pass through can cause large radiators not to heat up correctly and can make the system noisy as well as making the system less efficient.

Note: the manufactures do claim that these high restriction valves are made to the correct BS standard (BS 7478) and will Pass up to 4KW of heat on a Small bore (15mm) system. But it is worth keeping the restriction down to a minimum so there is more water flow through the boiler and system.

If you have a one pipe system you must always use a full flow valve as each radiator is fed only by gravity consequently, a larger bore means more hot water. Our advice is to get it re-piped as soon as possible into a normal 2 pipe system

The way to set up TRV's is to set each valve mid way. After the heating has been on for about 2 hours and if the air is too warm turn the valve down 1 number or 1/2 a number. Or if too cool up 1 number. Keep doing this until you find the right setting for each room. Touching the radiator will only tell you if it is on or not at that moment in time. Once you find the temperature you require, each time the heating is put on from cold, the radiator will come on fully and as the pre-determined room temperature is reached the TRV will turn the water flow off letting the radiator cool down. The TRV will then control the temperature of the room by opening and closing as necessary.