How to replace a TRV head

Inspired by a helpful YouTube guide. This walk-through draws on the PlumberParts video "Thermostatic Radiator Valves — Plumbing Tips" from the long-running UK plumbing advice channel. It explains how TRV heads work, which rooms to fit them in, and what to check if a radiator is stuck fully open or fully closed. Worth watching if you have never had to deal with one of these before.

1. Check whether the pin is stuck

Before buying a new TRV head, check whether the existing one is simply seized. The valve body has a small brass pin in the centre that the TRV head pushes down to open the radiator. If this pin is stuck in the down position, the radiator stays on regardless of the head setting — and if it is stuck up, the radiator will not heat at all.

With the heating off and the TRV head removed, try pressing the pin gently with a finger or a pencil. It should move smoothly in and out. If it is stuck down, a gentle tap with a light hammer and a small screwdriver usually frees it. Stuck up is rarer but sometimes penetrating fluid (WD-40 or similar) helps.

2. Choose a replacement TRV head

TRV heads are largely universal these days — most use either a RA (Danfoss-style) or a similar adaptor thread. Check the diameter of the valve body and whether it uses a clip-on or a threaded connection. Most modern replacements come with a range of adaptors to cover the main fittings.

Danfoss RA-type and Drayton heads are the most common in UK homes. If the valve body is old and a specific match is difficult to find, universal TRV heads from Screwfix, Toolstation, or a plumbing merchant will usually fit with the right adaptor in the pack.

3. Remove the old TRV head

Turn the dial to its lowest setting first. On a threaded connection, grip the valve body steady with one hand and unscrew the head anti-clockwise. It should come off without much force. On a clip-on fitting, there is usually a retaining ring or a small lever to release.

No water should come out at this stage — you are only removing the head, not disturbing the valve body or any pipe connections. If water does appear, the body has been disturbed; stop and call a plumber.

4. Fit the new TRV head

Select the correct adaptor from the pack, following the instructions that come with the replacement. Thread or clip the head onto the valve body and tighten gently by hand for threaded types — do not over-tighten. The head should sit snug but not cranked down hard.

Make sure the head is oriented so the dial faces outward and is easy to reach. Some valve bodies have a small arrow on them indicating flow direction — the head fits either way, but check the instructions if yours has a directional indicator.

5. Set the dial and test the radiator

Turn the heating on and set the new TRV dial to its maximum position. The radiator should begin to warm up within a few minutes. Once it is hot, reduce the dial setting progressively and check the radiator cools and reheats as you adjust it.

A setting of 3 on most TRV scales corresponds to roughly 20°C room temperature, which suits most living spaces. Bedrooms often benefit from a lower setting (1 or 2). The numbers are not precise thermometers — they are relative settings based on room temperature rather than water temperature.

When to call a handyman

Call Richard if the valve body itself is corroded or leaking, if the radiator still does not heat after fitting a new head and freeing the pin, or if you have a number of TRVs that need replacing around the house and want the job done in one visit.