Replace a leaking or worn thermostatic radiator valve safely, without draining the whole heating system.
RV-01Turn off the heating and let the radiator coolSwitch off the heating system and wait at least an hour for the radiator to cool. Hot water under pressure can scald you if a joint is disturbed while warm. Lay old towels and a shallow tray under the valve to catch drips.
RV-02Close both valves on the radiatorTurn the TRV to off and close the lockshield valve on the other end using a spanner or the little cap removed first. This isolates the radiator from the rest of the heating system so you don't need to drain it all. Note the lockshield's position or count the turns so you can set it back the same later.
RV-03Open the bleed valve to release pressureUse a radiator bleed key to crack open the bleed valve at the top of the radiator. This lets trapped air escape and confirms the radiator is properly isolated, since little or no water should come out.
RV-04Undo the TRV body from the pipeHold the pipe nut steady with one spanner and loosen the TRV body's cap nut with another. Have your tray ready underneath, as some water will still drain out of the pipe and radiator end. Loosen slowly rather than all at once.
RV-05Remove the old valve from the radiatorUnscrew the old TRV body from the radiator's threaded inlet. Wipe away any old jointing compound or PTFE tape from the thread. Check the thread isn't damaged, as this is where the new valve will seal.
RV-06Fit the new TRV body to the radiatorWrap PTFE tape clockwise around the radiator thread, 8 to 10 turns. Screw the new TRV body on by hand first, then tighten with a spanner until snug. Don't overtighten, as radiator threads are usually soft metal and can crack.
RV-07Reconnect the valve to the pipeFit a new fibre washer or olive to the pipe connection, following the valve maker's instructions. Push the pipe nut onto the new valve tail and tighten by hand, then a further half to three-quarter turn with a spanner. If it's a compression fitting, make sure the olive seats squarely before you tighten fully.
1 each · Fibre washer or replacement olive (per valve kit)
RV-08Reopen both valves and bleed the radiatorOpen the lockshield valve back to its original position, then turn the TRV to a mid setting. Use the bleed key to let trapped air out until water runs steadily, then close it. Check the boiler or system pressure gauge and top up if it's dropped, following your boiler's instructions.
RV-09Check every joint for leaksTurn the heating on and let the radiator heat up fully. Feel and look along the new valve's joints at the radiator and pipe for any dampness. Tighten gently if needed, then check again after 20 minutes, as small drips can appear once the joint has been under pressure a while.
RV-10Set the TRV and tidy upFit the thermostatic head onto the valve body and set it to your usual comfort level. Dry off any residual water, wring out and remove the towels, and dispose of the old valve. Wipe down the floor area to check nothing has been missed.
Some links may earn us a small commission at no extra cost to you.