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Thermostatic radiator valves not working

Postby Marty Boy » Thu Nov 18, 2010 10:21 pm

I can't control the temperature on one of my radiators using the thermostatic valve. When the heating is on the radiator is always extremely hot and if I turn the valve down or even off it doesn't make a any difference, it's still extremely hot. Is this something I can fix myself or does it require a plumber? Thanks
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Postby toplondonchef » Sun Nov 21, 2010 6:10 pm

Marty Boy
These thermostatic valves (TRV) can stick in the open or closed position especially after summer with no central heating on or if they are left on their setting and never turned up or down.
Set the TRV to the highest setting,ie. fully open and remove the top of the TRV by undoing the large thumbwheel just above the radiator tail pipe (this should be just hand tight and not require a wrench)
You will then see a metal piston which can sometimes sieze. You should be able to push this piston down and it should easily pop back up again. If it feels stuck or stiff try a squirt of WD40 and work the piston up and down several times to try to loosen it
If the piston is moving freely then the cartridge in the TRV head may have failed. Buy a new TRV and the head should screw onto the existing fitting between the supply pipe and radiator tail - just hand tight
If the piston is seized and you cant move it then the complete TRV will need replacing. This can be done with basic plumbing skills but will require the system to be drained down or take a gamble with a pipe freezing kit
TRVs benifit from being fully opened then closed several times,then set to desired number, at least twice a year to prevent piston seizure
I am not a plumber by the way but have had same problem which was simple to rectify
Good luck and hope that this helps
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Postby thedoctor » Fri Oct 30, 2015 12:33 pm

Hi All

We now have a handy guide on TRV's and thermostatic radiator valves that covers many of these questions and also how to fit and change a TRV. If you are interested you can find our TRV's project here.

Hope this helps
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Postby htg engineer » Fri Oct 30, 2015 9:04 pm

TRV's don't control the radiator temperature, the TRV head senses the room temperature and closes the valve when the desired temperature is met.

All radiators will be the same temperature, unless the TRV is closed.
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