Radiators have two valves – one at each end. On a basic set up, there will be a lockshield valve at one end and a user adjustable valve at the other. The lockshield is used primarily for balancing the system and has a cap over a square headed spindle which requires a spanner or wrench for adjustment. Under normal circumstances, you won’t need to touch this one. The other valve can be readily opened or closed by turning the valve head. This is used to adjust the heat output as required.
Thermostatic Radiator Valves
Thermostatic radiator valves offer more control and have a series of settings marked on the valve head. Inside the valve head, a thermostat opens and closes the valve by pushing against a pin according to the air temperature around it and the setting selected.
Whether you are changing a defective valve or replacing the standard one with a thermostatic valve, this guide explains the process. Remember that most thermostatic valves are fitted on the flow not the return. Bi-directional thermostatic valves are available allowing flow in either direction. The casing is usually marked to show the direction of flow. If you decide to fit thermostatic radiator valves you should either have one radiator without one or, a bypass on the system. The reason is that with all radiators having thermostatic valves it would be possible for all of them to be closed and, with the heating on, the pump would be trying to push water round a closed system.
Removing the Old Radiator Valve
Switch off the boiler and isolate from the electricity supply by removing the fuse. Allow the system to cool before carrying out any work. You will now need to drain down the heating system. See Draining Down Sealed Central Heating System or Draining Down Vented Central Heating System
Make sure that the new valve you have bought is the correct type and size, and that it will fit without having to make any modifications to the pipe work. If not you might be better off going back to the shop and getting a more suitable one. Valves from the same manufacturer will normally be compatible.
Lay some protective sheets below the radiator just in case of spillages. Water in heating systems can easily stain carpets. Make sure that the valve is in the open position. Position a plastic container under the joint to collect any remaining water. Plastic dustpans are ideal for this as they can be wedged up under the joint to catch any drips. Slacken the nut on the radiator side of the valve to be replaced. When undoing valves, hold the body of the valve with a wrench while you undo the joints and this will prevent twisting. Undo the bleed valve at the top of the radiator. This will allow air in, and any residual water to escape at the loosened joint. Undo the nut completely. Now undo the compression nut where the valve is connected to the pipe work and remove the valve.
You’ll now need to remove the old olive – the metal sealing ring on the pipe. This can sometimes be done with a little coaxing from a wrench. If not, you’ll need to cut it off carefully with a junior hacksaw. Cut at an angle and don’t damage the pipe itself. Clean the pipe end and fittings to remove any debris and dirt.
Fitting New Radiator Valve and Radiator Tail
Check that the new valve will fit on the radiator tail already in the radiator. If not, you will need to replace this first. This is usually undone with a hex key inserted into the tail end. Replace with the new radiator tail having wrapped the thread with a few turns of PTFE tape.
Place the compression nut for the new valve over the pipe followed by the new olive. Mount the new valve on the pipe and gently manoeuvre it to connect with the radiator side as well. This may require a little force but don’t overdo it.
Tighten the nut on the radiator connection side. Remember to hold the valve body with a wrench to prevent it twisting as you tighten the joint. As always, don’t over tighten. Now assemble the pipe side connection . Bring the compression nut up towards the valve. The olive will come with it and, as you tighten up the nut, will be compressed around the pipe to form a seal. As before, tight but not overdone. With all compression fittings, if there’s a very slight leak you can nip it up a bit, but not if the olive has been crushed and the seal broken.
Refilling and Bleeding the Radiator
Once you’re happy that everything is finished, close both radiator valves and the bleed valve at the top of the radiator. Make a note of how many turns are required to close the lockshield valve as you will need to open it the same amount later. If you don’t do this, you may have to rebalance the system. Now refill the system in the normal way and check there are no leaks. Open the new valve to allow water into this radiator and check again. If all is well, open the bleed valve so that the air escapes and the radiator can fill. Finally, open the lockshield valve the noted number of turns so that water can flow again.
With everything complete, the electrics to the boiler can be reconnected and the boiler switched on. Run the heating for a while and make a final inspection of the new fitting.