How to Replace a Thermostatic Radiator Valve (TRV)

6 min read

A seized, leaking or worn thermostatic radiator valve is a common heating fault — and replacing one is a job many confident DIYers can tackle. Here's what's involved, and when to call a professional.

When should you replace a TRV?

Replace a TRV if it's leaking around the body, the head won't turn or has snapped, the pin underneath is stuck and won't free up, or the valve no longer controls the radiator's temperature. If only the head is faulty but the valve body is sound, you may be able to fit a replacement head instead of the whole valve.

What you'll need

A genuine replacement TRV (matched to your pipe size — usually 10mm or 15mm — and angled or straight body), two adjustable spanners or a basin wrench, PTFE tape, a radiator bleed key, an old towel and a bowl to catch water. A complete radiator pack pairs the new TRV with a matching lockshield.

Step 1 — Isolate and drain

Turn off the heating and let the system cool. Close the TRV (or remove the head and fit a decorator's cap) and close the lockshield valve at the other end of the radiator, counting the turns so you can reopen it the same amount later. On a sealed system you can often just isolate that one radiator; on larger jobs you may need to drain down partially.

Step 2 — Remove the old valve

Place a towel and bowl underneath. Undo the cap nut connecting the valve to the radiator, then the nut on the pipe. Support the pipe so you don't strain it. Some water will escape — have your bowl ready. Lift the old valve away.

Step 3 — Fit the new TRV

Wrap PTFE tape around the threads, offer up the new Myson TRV2 valve and hand-tighten both nuts, then nip them up with a spanner while holding the valve body steady. Don't over-tighten — you can crack fittings. Myson TRV2 valves are bi-directional, so orientation of flow isn't a problem.

Step 4 — Refill, bleed and check

Reopen the lockshield the number of turns you counted, restore pressure/refill, then bleed the radiator to release trapped air. Turn the heating back on and check carefully for leaks around both connections, tightening a fraction more if needed.

When to call a heating engineer

If your system needs a full drain-down, the pipework is corroded, or you're not confident isolating and refilling the system, use a qualified heating engineer. It's a small cost for peace of mind against leaks and water damage.

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