Radiator valve stuck or broken? Here's what to replace

Signs the valve is stuck or broken

A thermostatic radiator valve (thermostaatkraan in Dutch) has two parts: the head you turn, with the numbers on it, and the valve body on the pipe. Milieu Centraal puts it simply: the head closes the radiator once the room reaches the set temperature, and setting 3 is about 20 degrees.

When it fails, you see one of these:

• The radiator stays cold whatever the head is set to, while other radiators are warm.
• The radiator stays hot and the room overheats, even on the lowest setting or the frost symbol.
• The head turns without any change: the numbers move, the radiator doesn’t.
• A weep at the valve: a wet patch or a green crust where the spindle comes out of the body, or a drip at the nut.
• The head is cracked or loose, or it has been knocked and no longer sits square.

The first three usually come down to the pin. The last two mean a new part.

Free the pin first

Before you buy anything, try this. After a summer switched off, the small pin under the head often sticks in the closed position. Turn the head fully open, take it off, and press the pin with your thumb. It should spring back up. If it’s stuck, work it gently in and out a few times; a light tap on the side of the body can help. Put the head back and try the radiator.

My guide to a radiator that won’t heat up has the full checks, including the balancing valve at the other end, which is the other common reason for a cold radiator. If the pin frees, you’re done, and it cost you nothing.

Replacing the head only

If the pin moves but the head no longer controls it, or the head is damaged, a new head is enough. The body stays on the pipe, so no water comes out and you don’t touch the boiler. It’s a few minutes’ work and a safe DIY job.

Two things to get right:

• The fitting. Heads aren’t universal. Many screw onto the body, some makes use their own clip. Send me a photo of the body, or take the old head with you to the shop.
• Where it goes. Milieu Centraal is clear that the radiators in the room with the room thermostat should have no thermostatic heads and stay fully open, otherwise the thermostat and the boiler fight each other. A plain head there is the right choice. My guide to choosing a thermostat covers smart radiator heads too, which are simply a different head on the same body.

Replacing the whole valve

The whole valve has to go when the pin won’t free, when the body weeps at the spindle or the nut, or when you’re swapping an old plain valve for a thermostatic one. That’s a different job, because the valve body is full of heating water under pressure.

What it involves: the radiator is isolated and drained, or the system is partly drained if the radiator can’t be isolated. The old body comes off the pipe and the radiator tail, the new one goes on, then the system is refilled, the radiator bled and the boiler pressure topped up. My guide to boiler pressure explains the topping up. Then the whole thing is checked for leaks while it heats.

That’s what I’d rather do for you. Draining, cutting into pipework and getting the pressure right again isn’t difficult for me, and it’s where a DIY attempt turns into a wet floor. It’s part of my radiator work.

If the whole house still has plain valves, there’s a reason to do it in one go: Milieu Centraal notes that since 10 March 2020, when the boiler is replaced, every room has to have its own temperature control. So valves often land on the quote for a new boiler. And if the system is being drained anyway, for example when a boiler is moved, the valves are cheap to do at the same time.

Presetting and balancing

A new valve isn’t the end of it. The hot water still has to be shared fairly between the radiators, and that’s balancing, waterzijdig inregelen in Dutch. Milieu Centraal explains it as spreading the warm water better over the whole system, and notes that it only works if every radiator has a balancing valve.

Where that valve sits depends on what’s fitted. Many thermostatic valve bodies have a preset ring under the head that limits how much water can pass: that’s the presetting. Older setups use the lockshield valve at the other end of the radiator, under a plastic cap. Either way, the radiators near the boiler are throttled back so the far ones get their share. It takes measuring and patience, and it’s part of my radiator work when I fit a set of valves.

One more thing, from the boiler’s side. The Intergas installation manual says that when every radiator has a thermostatic or closable valve, a minimum flow of water through the boiler has to be guaranteed. In practice that usually means a bypass or one radiator that stays open, which is why the living-room advice above matters for the boiler as well as for comfort.

What it costs

My rate is €114.95 incl. BTW per hour, with no call-out charge. Valves and heads are materials, listed separately on the invoice.

Replacing one valve body means draining and refilling as well, so allow for more than a head swap. For a set through the house, send me the number of radiators and a photo of each valve, and I’ll plan it as one job, with the balancing done at the end. My prices page has the full rates.

Send me photos

Message me on WhatsApp with a close-up of the valve body and head, a photo of the whole radiator, the valve at the other end, and the boiler’s pressure reading, plus your postcode. I’ll tell you whether it’s a head, a body or just a stuck pin, and what it will cost.

If you smell gas, leave the property and call 0800 9009 from outside. If a CO alarm goes off, get everyone outside and call 112.