My house had a new gas central heating system fitted, with new radiators, before I moved in. One radiator (in the tiny downstairs WC) is missing the control knob for the TRV, and is set to the highest setting. I vaguely remember seeing somewhere that this is desirable for some reason, but it is far too hot for such a small room.

I haven't been able to find a replacement control without the entire TRV, so is it safe to lower the heat using an adjustable wrench or something?

2 Answers 2


Until you get it replaced you can adjust the radiator temperature by adjusting the balancing valve on the other side of the radiator. Open the plastic cap and use a adjustable spanner and close the valve clockwise as necessary! good luck.

-unicuk, How to replace a Thermostatic radiator valve (broken Head).mp4 , YouTube

As I understand it, TRVs operate by depressing the little pin, in increments. You need to check this for free movement before buying just a knob replacement. The nut your probably looking at would disassemble the TRV. Look for a valve on the opposite side and turn that one.

This is from research, not experience, good luck.

  • After reading your answer I think the end that would have a TRV is actually covered up, and I'm looking at the balancing valve. Thank you!
    – conradj
    Commented Oct 10, 2014 at 7:56

I think on some systems at least one radiator should remain open to provide some circulation - maybe for the sake of the pump. This valve wouldn't have a TRV or the setting would be very high so it wouldn't ever close fully. Would that be why it's covered up?

The tiny radiator would be a good choice as it would dissipate and waste least heat.

  • 1
    Correct as to why you need one radiator always open. As to choice of which one: the best is the one in the room which has the house thermostat; the house thermostat therefore shutting off supply to that radiator (and all other radiators) when that room is warm enough.
    – AndyT
    Commented Nov 27, 2015 at 10:14
  • If the heating system has a weather control (temp sensor outside), the best choice for free flow radiators will be all the bathrooms, as these are the rooms we want warm all the time.
    – Thomas
    Commented Nov 30, 2023 at 11:08

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