How to fix thermostatic radiator valves

Thermostatic radiator valves are very reliable but on rare occasion that you get an issue with TRVs here’s a quick rundown of potential problems and how to fix them.

How do thermostatic radiator valves work?

Before we fix something, its always good to know how something works. Depending on how you set the valve, it adjusts the flow of water that goes into your radiator from the boiler.

As the room heats up, a capsule in the valve head expands, which moves a pin in the valve body that causes it to close, which means it receives less hot water into the radiator. As the room then cools, the capsule in the head contracts again, pulling the pin out of the valve body, allowing hot water to enter the radiator again.

Two types of TRV design

Thermostatic radiator valves come in two main designs: with either a wax or liquid capsule.

Liquid TRV design

A liquid thermostatic radiator valve is the technically more efficient model, as liquid is more responsive to room temperature changes than wax. This means your room heats up quicker.

Wax TRV design

The wax capsule in older TRVs is slower to expand and contract in response to the room temperature, and are therefore cheaper.

Stuck thermostatic radiator valve

A sticking valve is probably the most common issue you may encounter with thermostatic radiator valves. You may find that it stuck open or closed. You usually find a TRV becoming stuck after a long period of not being adjusted, either after a long, cold winter or a long, hot summer.

How to fix a stuck thermostatic radiator valve:
1. Set your TRV to the highest setting.
2. Unscrew the thermostat removal nut by hand. Underneath is a piston that will usually spring up at this point and you’ll be able to push it down and up again smoothly (ideally).
3. Get a can of WD40 and spray a little on until the piston moves smoothly again.
4. If the piston doesn’t loosen up, you’ll have to replace your TRV.

How to avoid it: Keep your TRV in tip-top condition by occasionally lubricating the valve piston with WD40 – perhaps once a year before the big heating switch-on. This will protect it from sticking.

Thermostatic valve not switching on or off

If your thermostatic radiator valve isnt turning on or off and you have checked to see is its stuck unsing the information above and the piston’s moving smoothly but your TRV isn’t actually working, its components are most probably worn out or broken. This is more likely if it’s an older TRV, its time replace it with a new one as you can not repair them. If the piston is moving smoothly then you can simply replace the thermostic head of the valve and not have to replace the whole valve, so no plumbing work is involved.

How to avoid this: It may be that your valve head vents have got clogged by dust and other debris. When this happens it obstructs the air that hits the liquid or wax capsule inside (which will mess up the readings). So do yearly checks and clear any dust or debris.

Room not warm enough

TRV’s should be located in a free movement of ambient air so it can monitor the air temperature correctly, TRVs which are located in enclosed areas or behind long curtains can suffer from premature close down preventing the room from reaching its ideal temperature.

Location of TRVs

Obviously TRVs should be installed on the inlet or outlet of the radiator, older TRVs had a directional arrow indicating the direction of flow with which they operate, if the TRV was installed with the direction of flow in the wrong direction nuisance banging could be heard as the valve attempted to close down. Modern TRVs are bi-directional meaning they will work correctly irrespective of the direction of the flow.

TRVs should be installed on every radiator except the reference radiator or the radiator in the same location as the room thermostat. It is important that the reference radiator remains controlled by the wheel head valves only and allows the room thermostat to control the entire heating system correctly.

TRVs should not be installed on all radiators unless a suitable system bypass is installed between the flow and return and a suitable system interlock, a device that will shut off the heating once the desired temperature has been reached i.e. a room thermostat, is also installed.

We hope you find the above imformation helpfull in repairing or diagnosing your thermostatic radiator valves.