I'm doing some decorating at home and needed to remove the radiator. I still need to be able to use the gas heating throughout the house while the radiator is off.

I closed the TRV and lockshield valve, I then loosened the lockshieled valve nut and proceeded to drain the radiator. Once empty I removed and all was well.

My gas boiler was at 1.5 bar before this work, and 0 after - I expected this. I topped up the boiler pressure slightly to around 0.5 (by opening the valves), then I had a quick look at the radiator pipes and noticed that the lockshield valve side was leaking, a constant dribble of water. The water was coming out of the lockshield valve housing (the threaded part where the radiator connects). Image attached.

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Was this because I repressurised the gas boiler? Should I have capped off this lockshield valve housing somehow one the radiator was removed?

I panicked and put on the radiator again! So, not sure where to go from here really :/ My gas pressure is now at 0 again, although I still had hot water this morning.

Any advice is appreciated.

1 Answer 1


Seems your TRV was allowing a small flow to maintain the temperature of the (disconnected) radiator.

Try capping the open end of the pipe, the male end in your illustration.

Your local hardware store will have the right sized cap; take a cell-phone photo of the threaded open end with a ruler placed next to it, at the maximum width of the threads. To be certain, do the same with the radiator's end of the connection.

This should stop the TRV's flow (your "leak") and allow your boiler pressure to rise to normal while you have the radiator detached.

  • Thanks for this information, very helpful! Maybe i'm confused, but isn't the TRV the big one at the other end that has the numbers (1 - 5) to control the heat? The leak was coming from the opposite end, as can be seen in my image. I'll go buy a cap today, fit in and try repressurise the boiler again. Is this what I need (i'll measure size when I get home) screwfix.com/p/blank-nut-x/…
    – jonboy
    Oct 21, 2019 at 11:17
  • The TRV controls the flow of water through the radiator. The vast majority of new TRV's are bidirectional and can be fitted to either the flow or return, but they are usually installed on the flow side. But maybe yours is on the other side of the radiator. In any case, capping it while disconnected will allow you to do your decorating without worry. Oct 21, 2019 at 13:44

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