Lesson 14

Joints & Sealing

Find which of the seals on a radiator valve is leaking, understand how each one seals, and know what to report rather than tighten.

Builds on

Emergencies & Shutoffs
Changing a TRV Head

Four seals on one valve

Kai finds a drip hanging under the valve on his lounge radiator, and a damp patch on the carpet below. A radiator valve looks like one lump of brass, but it seals water in at four separate places, each with its own nut:

where the pipe from the floor enters the valve: a compression joint;
where the valve meets the radiator tail, a short pipe screwed into the radiator: a union;
where that tail screws into the radiator itself: a thread with a sealant or washer;
where the valve’s spindle passes up into the head: the gland.

The threads on a nut don’t always make the seal. Often they just pull together the two surfaces that do. Knowing which surfaces seal is how you find a leak, and how a plumber fixes it.