How To Change A Radiator Thermostat

First thing to do is turn off the power supply to your boiler. This prevents the heating system from calling for heat while you work. If you have a combi boiler you'll need to release the pressure to the radiator. 

• Take your radiator key and turn the bleed valve anti-clockwise.

• Water will drain from the valve releasing the pressure so be sure to hold something like a bucket directly beneath it to catch the water.
• Once the water has slowed to a trickle, turn the bleed valve back to its original position.

For gravity-fed systems, you'll need to get access to your header tank which is in your loft.

• Remove the lid of the header tank to access the two pipes. These are the expansion vent pipe and cold water feed pipe.

• Position the tank bungs over the end of the pipes, ensuring a tight seal to pull a vacuum.

   

With the pipes in the cold water tank now properly sealed you can return back to your radiator.

• Open the TRV you are replacing and turn off the lock shield valve by removing the cap, then turning it clockwise.
• This will isolate the radiator and prevent water from flowing when you remove the valve.

Now it's time to test that a vacuum is being created at the cold water tank. This is important to prevent water leaking everywhere when you remove the old radiator valve.

• As you did in step 1, grab your radiator key and open up the bleed valve on the radiator. Make sure to hold something underneath to capture any water.
• Observe the water flow; it should reduce significantly, confirming that the vacuum is effective.
• Do the bleed valve back up and move on to the next step.

It's a good idea to prepare the new radiator valve before taking off the old one as, in the event of excess water leaking from the system, it's quick to attach the new valve. 

• Remove the nuts and olives from the new TRV.
• Keep the decorator's cap on the valve to prevent water from leaking out during the installation.

Using an adjustable spanner, carefully loosen off the bottom nut of the old TRV. Make sure there's something underneath to catch any water run off.

You now need to loosen off the top nut. But, before doing so, use some suitable grips, like waterpump pliers, to firmly grasp the main part of the valve. This prevents the pipework from becoming misshapen. 

• Ensure a firm grip on the valve with the waterpump pliers.
• Use your adjustable spanner to loosen off the top nut, then use your fingers to wind it back a little. 
• The old valve should now be completely loosened off and ready for removal.

Carefully twist and pull out the old radiator valve. You may need to further loosen off the bottom valve to completely remove it. Once removed, you'll get a slow, steady flow of water, but don't worry as that's expected.

You'll want to move fairly quickly at this step to maintain the vacuum and prevent significant water run off.

Grab your new radiator valve and quickly pop it into place making sure that the orientation is correct. You'll know as the arrow on the valve should point in the direction of flow. 

• Hand-tighten both the top and bottom nuts
• Using your adjustable spanner, tighten them up fully. You can use the waterpump pliers to hold the valve steady when you do this.

Before turning the boiler back on, check all connections for leaks. Tighten any loose nuts as necessary.

Remove the bungs from the header tank, replace the lid, and turn the boiler back on. Wait for a few minutes before testing the radiator.