UK trade guideRadiator & Heating 5 min readUpdated 9 July 2026

How to Replace a Radiator Valve (UK)

Fit a new manual or thermostatic radiator valve. 15 mm compression, 1/2" or 3/4" tail sizes.

HoneywellDraytonDanfossPegler

Angled vs straight

Angled — pipe rises up from floor to a rad with side inlet. Straight — pipe emerges from wall behind the rad. Measure before ordering.

Fit

Drain rad only using freeze kit or full drain. Undo old valve nut, remove old tail from rad. Wind PTFE 6 turns clockwise on new tail. Fit and tighten.

Frequently asked questions

Which tail should I fit — 1/2" or 3/4"?
Measure the rad tapping — 1/2" for panel rads (most), 3/4" for cast iron and towel rails.
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