There are barely any instructions in the manual. Do I need more than a spanner to do replacement?

Is it necessary to shut off the water supply to the radiator in order to replace the radiator valve?

  • 2
    Often two spanners so you don’t hold the plastic body but the valve body.
    – Solar Mike
    Commented Feb 22, 2020 at 20:02
  • 4
    Quick check: Did you know that it is possible to replace the plastic part, including the thermostat, very quickly without any water leaking, and without any tools? Exactly how it is done depends on the brand. If it's just not working, or the plastic part is jammed, or got knocked and broken, this is usually fixes it.
    – Jack B
    Commented Feb 23, 2020 at 14:22
  • 1
    What Jack B said! You are only likely to have to replace the whole valve if it got physically damaged somehow, or it is leaking water. The usual problem is the thermostat part stops working. In the valve in your picture, unscrew the metal ring above the 90 degree angle, right underneath the plastic part. You should be able to do that with your fingers unless it is very tight. The plastic top then lifts off without leaking any water. Inside there will be a small pin that should be free to move up and down, but often gets stuck. Often, just loosening the metal ring is enough to unstick it.
    – alephzero
    Commented Feb 23, 2020 at 19:46

3 Answers 3


You need to drain the water from the heating system, effect the remove and replace, then refill the heating system.

Some circulating-water heating systems are filled with tap water from the home's water supply, while others are isolated from the water supply plumbing and are filled with some other liquid. My experience is entirely with the most common tap water type, so I cannot tell you how to empty and refill an isolated system.

If you have a tap water connected system, you need to find three connections on your heating system, one where the water is admitted, one where it can be drained, and one where air can bled from the system.

The water will be admitted into your heating system from your home's cold water pipes, at a connection with a valve, pressure regulator, and probably a backflow preventer. Look for a pipe from the house plumbing into the furnace or into the pipes near the furnace. Look for a pipe interrupted by a valve and one or two other fittings.

The water can be drained from your heating system via a faucet or similar valve near the bottom of your furnace. It will have threads on its spout to accept a garden hose. Attach a hose to this faucet and place the other end of the hose outside your house, at a point lower than the bottom of the furnace.

The air bleed valve is usually found at the top of each radiator. These rarely have a handle attached; you are supposed to open it with a small spanner or a special key.

To empty the heating system: turn the furnace off, close the admitting valve, open the drain faucet, and open the highest air bleed valve in the house. Wait until water stops flowing from the end of the hose.

Use two spanners to remove the broken thermostat valve, and to install the new one.

To refill the heating system: close the drain faucet, open the admitting valve, and wait by the air bleed valve with a pan or bucket until water comes out, then close the air bleed valve. Now visit every radiator in the house, open its air bleed valve, wait with your bucket to catch the water that comes out, and close the valve.

If you have trouble confidently locating these places on your heating system, take some photos and post them here. Include a picture of one of your radiators, so you can get specific pointers from someone who has experience with your make and model.

  • 4
    In colder climates, antifreeze (not toxic ethylene glycol) is commonly added to the water in the system. If you drain the water, replacing it with just water can cause your pipes to freeze and break. (Don't ask me how I know that. ;-) Commented Feb 23, 2020 at 3:40
  • @Mike Waters: If this is the case then OP will not be able to find an admitting valve. Commented Feb 23, 2020 at 3:54
  • 1
    Why do you say that? My system had one. Commented Feb 23, 2020 at 3:58
  • 1
    @Mike Waters: Could you please post an answer explaining how to drain and refill such a heating system? I don't want to lead OP astray and burst his pipes. Commented Feb 23, 2020 at 4:05
  • Many thanks for the input. I have learned a good ideal about heaters from your detailed answer. I think I will get my landlord to send a professional for this job, I prefer not to take any risks here. Commented Feb 24, 2020 at 10:22

Heating systems can vary by region. I have answered this from a UK perspective as you appear to have bought from B&Q.

If the broken part is the white thermostatic cap, then it would be much easier to find a compatible replacement to avoid having to change the valve body. The cap can be removed by undoing the knurled ring directly below it, finger force only is required. On all the ones I have seen, the cap can be removed without water leaking.

If the valve stem has broken then you will need to replace with a complete new assembly.

This isn't a difficult job if you are comfortable with plumbing connections and heating circuits, but there can be complications and there are real risks of leaks, minor floods or system damage if you make a mistake. The water in the bottom of radiators can sometimes be filthy and contain sludge. If it gets onto your floor it will make a mess. If you are unsure, then ask a heating engineer or plumber to do this.

Rather than me explain in detail how to do this, I recommend watching some videos and reading some guides. For example: https://youtu.be/oMXgKXVZw_0

In summary though, you will need to turn off the boiler, turn off the fresh water supply to the boiler and heating circuit, drain the water from this radiator and possibly the other radiators in your house, remove the old valve and possibly the tail pipe between the valve and radiator, replace with the new parts and refill the heating circuit, adding corrosion inhibitor. As the system refills, check for leaks and bleed off the air. Remember not to leave any bleed valves open. Only turn on the boiler when you are sure the system is full of water. It might take hours or weeks for any remaining air to gradually find the high points and allow you bleed it all out.

You will need a spanner for the valve nuts, an adjustable spanner to hold the valve body when you loosen or tighten the nuts, a spanner or key appropriate for the existing radiator tail and also for your new one, a drain off hose and key, a bleed key, some PTFE tape for the tail to radiator joint and some corrosion inhibitor fluid. Also have plenty of rags or old sheets on hand just in case.

Be mindful of:

  • Check that the valve you have bought uses the same pipe diameter as your old one. In the UK, this is usually 8 mm, 10 mm or 15 mm.
  • From the B&Q site it looks like your valve is bi-directional. It should have a double ended arrow on the chrome body. These can be used on either end of the radiator. Some valves are not bi-directional and the water flow must match the arrow.
  • The drain down and refill method depends on whether your system is sealed or open vented.
  • Avoid twisting the valve body and pipes when you turn the nuts. Hold the body with an adjustable spanner.
  • Be prepared for some remaining water or sludge when you loosen the valve and remove the tail.
  • There are tools that allow you to change a valve without draining as much water. They have a much higher risk of flooding your floor. I don't recommend them.
  • Remember, if you have a problem, you may be without heating and hot water until you can fix the problem, buy additional parts or get someone to help you.

It is possible to buy special 'freezer packs' that are designed to fit round pipework, with the intention of locally freezing the contents of the pipe, causing a temporary blockage.

Having said that, I would be rather wary of using them, (and have never done so) as the result if you get it wrong would be some catastrophic and messy flooding.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.