How to change a Radiator Valve

Fitting a new radiator valve when one breaks doesn’t have to be either stressful or expensive because you can often change a radiator valve yourself quickly and easily. Learn how to change a radiator valve in a few simple steps without the risk of flooding your home in our guide.

When to change a radiator valve

The key sign that you need to change a radiator valve is a single radiator failing to heat up when you aren’t experiencing any other problems with your plumbing. However, before you go ahead and replace it, there are a few checks that you can do to make certain the problem is actually with your valve.

First, you should check that the original valve is fitted correctly. Most thermostatic radiator valves are now universal but older models will have an arrow indicating the direction of flow. If your radiator has previously worked with no issues, then you can assume that it will be fitted correctly.

Next, you should check to see if the valve has seized by removing the top and checking to see if the plunger can be depressed - it may be necessary to oil this. If it still doesn’t move after doing so, then you will almost definitely have to replace it.

If the valve is moving freely and the radiator works when the thermostat cap is taken off, the problem is likely the thermostat which you can replace separately. Although, you might want to take this opportunity to upgrade the entire valve.

If the plunger seems fine and the radiator is not working even without the thermostat cap, then the problem is likely an airlock or blockage – not your valve – and you may have to call a plumber.

Draining a central heating system

The most common way of making sure you don’t accidentally flood your home when working on your radiators is to drain your system. While other methods may be simpler, draining your system also allows you to flush out any sludge that has built up from iron oxide and water deposits.

This is fairly simple for a combi boiler, but for a conventional cylinder tank it may not be possible without professional help.

First, you should shut off the water to your heating system and electrically turn everything off. Make sure you turn down all thermostats so they are not calling for more heat – this could turn the pump on while the system is dry which could permanently damage it.

Next, you should find a system drain cock and make sure that it’s ‘downstream’ of the radiator you want to work on. You should be able to easily connect a hose to this drain valve and run it to a suitable drain. It’s best to put a towel down underneath the drain-off valve before you undo it to catch any drips.

Undo all the radiator bleeds in your system to let air in so that it can drain fully and so water isn’t trapped inside by a vacuum. You should leave this for around 15 minutes to drain fully.

Isolating a radiator

If you can’t drain your system (or decide not to), you can isolate your radiator instead. One of the best ways to do this is by closing the valve at the other side of your radiator (the one that you are not removing) and using a freezing kit on the pipe that’s connected to the valve you’re removing to prevent water from flowing.

As long as you bleed off any excess pressure before you start, and remember to close the bleed valve afterwards, the vacuum should hold the water inside the radiator. This should hold it long enough for you to attach a valve clamp (or bung) over the exposed end to hold the water in while you remove the valve.

The freeze blockage on the pipe connecting the valve to the system should stop water from passing in that direction. However, you will have to work relatively fast as it can thaw in around 15 minutes after application.

How to change a radiator valve

After you have drained your system – or started isolating your radiator – it is quite easy at this point to remove a thermostatic radiator valve.

First, put another towel down to catch any drips. Then, hold the body of the valve firmly with a grip clamp while unscrewing the nut on the radiator side. If you’re isolating your radiator, then you should block the exposed radiator fitting so that you don’t risk water flowing out while you’re working.

Holding the body again, you can now unscrew the nut at the bottom of the valve and remove it completely.

You should then clean the pipes and joints with a cloth before adding pipe joint compound to the threads of your new valve, being careful to only apply onto the male threads and not get any inside the pipe. This pipe dope will help to create a watertight seal to avoid any leakage once your system is running.

After this, you simply need to attach your new valve where the old one was. Although most modern valves are universal, you should still make certain. If it isn’t universal, then ensure that the valve is the correct way around for the flow of your system.

Refilling a central heating system

The first step in refilling your heating system is to make sure that you have closed all your radiator bleeds and your drain cock. It’s best to double check this so that you don’t end up with any leakage.

Gravity-fed systems can be filled easily by turning on the water supply to the heating system and then bleeding your radiators one by one so that they are properly filled.

Pressurised systems can be a little more difficult. For these, you should begin by pressurising the system up to 1 bar and then bleeding off your radiators. This will cause the pressure to drop and you will need to keep re-pressurising the system until you have successfully bled all your radiators.

Once you have successfully filled your system, you should check that there are no leaks. If it’s leak-free, you can introduce additives, such as inhibitors, to protect your system from corrosion or sludge build-up. It’s best to check for leaks first as inhibitors can be expensive and if there are leaks you may have to re-drain your system in order to properly fix them.

Top tips for fitting radiator valves

  • Make sure that the pipe joint compound you are using is designed for water, not gas.
  • Always double check whether your radiator bleeds are open or closed.
  • Make sure you always have a towel down to catch drips.
  • Always be prepared for your system to spill water even if you think you’ve fully drained it.
  • Thermostatic radiator valves can be attached to either side of a radiator and should be situated where it has easy access and good air flow to accurately measure room temperature.