How to Fit a Thermostatic Radiator Valve (TRV) — UK Guide

Drain down or freeze?

For a single TRV swap on a sealed system, a pipe freeze kit saves 40 minutes vs a full drain. Freeze both flow and return 300 mm from the valve; the ice plug holds for approximately 20 minutes at 20 °C ambient.

Bi-directional heads matter

Older TRVs are direction-sensitive — fit them backwards and the valve chatters. Any modern bi-directional head (Honeywell VT117, Drayton TRV4, Danfoss RAS-C2) can fit either flow or return. Always fit on the flow side where possible for the fastest response.

Recommended UK TRVs

• Honeywell VT117 — 15 mm, straight, bi-directional. Trade favourite.
• Drayton RT414 — TRV4 body with liquid sensor.
• Danfoss RAS-C2 — click-fit head, best low-noise performance.
• Salus HTRP-RF — programmable RF head for zoned smart control.