Thermostatic Radiator Valve Stuck: How to Free It

How to tell the valve is stuck, not the boiler

A stuck valve shows up in one of two ways. Stuck shut: the radiator stays cold whatever number you set, while the pipe feeding the valve is hot. Stuck open: the radiator is always hot, even on the lowest setting in a warm room. Stuck shut is far more common, and it tends to appear on the first cold week of autumn after the heating has been off all summer.

If several radiators are cold at once, look at the boiler and pump first. Our guide to radiator not heating up sets out that order. A stuck valve is a single-radiator fault.

Taking the head off

Turn the head to its highest number first. This pulls the internal plunger back and takes the pressure off the pin, which makes the head easier to remove and less likely to be damaged.

Most heads come off in one of three ways. Many have a knurled collar at the base that unscrews anticlockwise by hand. Some have a threaded nut that needs an adjustable spanner, held gently. Others clip on and are released by loosening a small screw on a clamping ring or pressing a release catch. If the head does not turn or unclip easily, look closely at the base for a screw or catch before forcing it.

With the head off you will see the valve body with a short metal pin sticking up from the centre, or sitting flush if it is stuck down. On a standard TRV the head only presses on the pin; the heating water is sealed inside the valve body by the gland around the pin, so taking the head off is safe with the system full.

Do not pull the pin out of the valve, and do not undo the brass gland nut around it. That is what keeps the water in.

Freeing the pin, step by step

A healthy pin moves down a few millimetres when pressed and springs back up by itself. A stuck one stays down, or will not go down at all. Work through these in order and stop as soon as it moves freely.

• Press the pin down firmly with your thumb or the flat of a spanner and let go. Repeat ten or twenty times. Often this alone breaks the scale holding it
• Tap the side of the pin lightly with the back of a spanner or a small hammer handle, then press again
• Grip the tip of the pin with pliers and move it gently up and down, and a little side to side. Do not twist it hard or pull up sharply
• With the heating on, listen and feel: when the pin lifts you should hear water start to flow and the radiator should begin warming within a few minutes
• Press the pin a few more times to check it now springs back every time, then refit the head at its highest setting and turn it down to where you want it

When freeing it does not work

Some pins are too far gone. If you have pressed and worked it and it stays down, or if it moves but sticks again the next day, the valve insert is worn or furred up with scale. Forcing it harder usually ends with a weeping gland, not a free pin.

Other signs the valve needs replacing rather than freeing: water weeping from around the pin or the gland nut, a pin that is bent or loose, a body so corroded the head will not seat, or a head that no longer responds to the room temperature even with a free pin. A head that clicks but does nothing may just need a new head, which is a cheaper fix than the valve body. The guide to how a TRV works explains what each part does.

Replacing the valve body means cutting off the flow to that radiator. An engineer will close the lockshield, isolate or partly drain the circuit, or use a pipe-freezing kit so the rest of the house stays full. On a sealed system the pressure is then topped back up and the radiator bled. Our radiator repair page covers the visit.

Stuck open, and radiators that are always hot

A pin stuck up means the valve cannot close, so the radiator runs at full output. It is wasteful but not urgent. Try the same freeing steps, pressing the pin down repeatedly. If the head is the problem rather than the pin, the sensor inside may have failed and the head alone can be replaced.

If every room runs too hot whatever the heads are set to, check a few pins first, then the boiler flow temperature and the room thermostat. Our guide to a boiler thermostat not working covers the controls end.

Costs, and stopping it happening again

As typical UK market prices, a replacement TRV head costs from about £10 to £30, a full valve from about £15 to £50, and a plumber fitting a new valve usually charges around £100 to £200 including the drain-down and refill. The £60 call-out covers any hour, and the repair price is agreed with you on site before any work starts.

To stop pins seizing over summer, turn every TRV to its highest setting when you switch the heating off for the season. That keeps the pin up and away from its seat. Running the heating briefly once a month in the warm months also keeps pins and the pump moving.