BoilerFaultCodesRadiator valve not working? It is almost always a stuck pin.
Thermostatic radiator valves seize shut over summer, because they sit in one position for months with nothing moving. Come October the radiator stays stone cold while every other one in the house heats up. The fix takes two minutes and costs nothing.
Free the pin
Turn the valve head to maximum
Wind it fully open first. If the radiator warms up on its own after ten minutes, the valve was just closed and you are done.
Pull the plastic head off
Unscrew the retaining ring at the base of the numbered head, usually by hand or with a gentle turn of pliers, and lift the head away. Nothing leaks when you do this. The head is only a temperature sensor pressing on a pin.
Find the metal pin
Under the head is a small pin, a few millimetres proud of the valve body. That pin opening and closing is what lets water into the radiator.
Press it
It should move down and spring straight back. If it is solid, or it goes down and stays down, that is your fault.
Work it loose
Grip the pin with pliers and gently pull it up, then work it up and down a few times until it springs freely. Tapping the side of the valve body lightly with the handle of a screwdriver often helps. A squirt of penetrating oil can free a stubborn one, though give it a few minutes to work.
Refit the head with the valve open
Put the head back on set to maximum, then turn it down to where you want it. The radiator should start warming within ten minutes.
Stop it happening again
Leave your radiator valves fully open through the summer rather than wound shut. A valve that spends five months open is far less likely to seize than one clamped closed. Some people run the heating for ten minutes once a month in summer for the same reason, which also exercises the pump.
What the numbers mean
The numbers are not heat settings, and this trips people up. They are target room temperatures. Setting a valve to 5 does not make the radiator hotter, it makes the valve stay open until the room is warmer.
| Setting | Roughly | Suits |
|---|---|---|
| ❄ (frost) | 5 to 8°C | Empty rooms. Stops pipes freezing without heating the space. |
| 1 | 10°C | Rarely used rooms |
| 2 | 15°C | Hallways, utility |
| 3 | 20°C | Living rooms. The usual setting. |
| 4 | 25°C | Warmer than most people need |
| 5 | 28°C+ | Valve stays open almost permanently |
Figures are the usual manufacturer mapping and vary slightly by make. Never fit a thermostatic valve on the radiator in the same room as the main room thermostat, because the two fight each other.
When freeing the pin does not work
The pin is seized solid
If it will not move with pliers and penetrating oil, the valve body needs replacing. That means draining down enough of the system to swap it, so it is an engineer job unless you are confident. Around £90 to £150 fitted.
The pin moves freely but the radiator is still cold
Then flow is the problem rather than the valve. Check the lockshield at the other end is open, and work through the wider cold radiator checks.
Cold radiator diagnosis →The radiator is stuck on and will not turn off
A pin jammed in the open position, or a head that has failed. The radiator will run hot whenever the heating is on. Same fix, same replacement cost if the pin will not free.
Water appeared when I took the head off
That should not happen and it means the valve is damaged. Put the head back on, turn it fully open to keep the pin down, and get an engineer out.
The other valve on the radiator
The end without the numbered head is the lockshield, usually hidden under a plain plastic cap. It is not a tap for daily use. It is set once when the system is balanced, to control how much flow that radiator takes compared with the others. If someone has closed it, the radiator goes cold. Opening it fully is not the answer either, because that steals flow from the rest of the house.
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