How to replace a radiator

Inspired by a helpful YouTube guide. This guide draws on “Replacing a radiator” from the Ultimate Handyman channel, a long-running and well-regarded UK DIY resource. The video is straightforward and deals honestly with the parts that go wrong — including the surprise of how much water a single radiator can contain. Recommended viewing before you get the towels out.

1. Turn the heating off and let it cool

Never work on a hot system. Turn off the boiler and wait at least an hour. Radiator water can be scalding and the system holds pressure when warm. Not worth rushing.

While you are waiting, lay down old towels or dust sheets around the base of the radiator and get a couple of old bowls or a washing-up bowl ready. There will be water — probably more than you expect.

2. Close the radiator valves

At one end of the radiator you will have a TRV (thermostatic radiator valve) or a manual wheel valve. At the other end, a lockshield valve with a plastic cap. Close both fully. The TRV turns clockwise to zero. The lockshield cap comes off with a pull or a twist, revealing a small spindle — count how many turns it takes to close it and note this down. You will reopen it the same number of turns when refitting, which helps balance the system.

3. Drain the radiator

Put a bowl under the TRV end. Use a radiator bleed key to open the bleed valve at the top of the radiator — just a quarter turn. Then, using an adjustable spanner, slowly loosen the union nut connecting the TRV to the radiator. Water will start to drain out. Guide it into the bowl.

When the flow slows, open the bleed valve a little more to let air in and speed drainage. Keep swapping and emptying bowls. An average single radiator holds somewhere between 2 and 5 litres, depending on its size.

4. Disconnect the union fittings

Once drained, fully undo both union nuts — one at the TRV end, one at the lockshield end. Hold the valve body with one spanner while you loosen the union nut with another to stop the valve rotating in the pipe. Water will dribble from the pipe ends; have your bowls underneath.

The tail pieces (the short threaded connectors that screw into the radiator) usually stay with the radiator. Keep them if the new radiator uses the same thread size.

5. Lift the radiator off the brackets

Wall-hung radiators sit on two or four brackets with a keyhole slot. Lift the radiator straight up — it should come off cleanly. They are heavier than they look. Get someone to help if it is a double panel or a long run.

Once it is off, tip any remaining water into the bowl and set the old radiator aside. Take a photo of the bracket positions before you remove them, in case the new radiator needs a slightly different spacing.

6. Reposition or replace the wall brackets

Check whether the new radiator’s bracket holes match the existing positions. If so, you can reuse the brackets. If not, fill the old holes and drill new ones. Radiator brackets should be fixed into solid masonry or, on a stud wall, directly into studs. The weight of a full radiator is not trivial.

Fit the tail pieces into the new radiator before hanging it — doing it afterwards while it is on the wall is awkward. Use PTFE tape on the threads, and tighten firmly with a radiator spanner.

7. Hang the new radiator

Lift the new radiator onto the brackets. It should drop into place cleanly. Reconnect the union nuts at both valve ends — hand-tight first, then firm with a spanner. Do not overtighten; you just need a good seal on the olive or the fibre washer inside the union.

8. Refill and check pressure

Open both valves: the TRV to the desired setting, the lockshield to the same number of turns you noted earlier. If your system has a filling loop (usually a small braided hose near the boiler), top up the boiler pressure to around 1 to 1.5 bar on the gauge. On an older header tank system, the tank will refill on its own.

Turn the heating back on and wait for the system to come up to temperature.

9. Bleed the new radiator

Once the system is hot, use a bleed key to release any trapped air from the new radiator. Open the bleed valve slowly until water drips out, then close it. Check the boiler pressure again — it may have dropped slightly after bleeding. Top up if needed.

Check all the union connections for any seeping while the system is hot and under pressure. Dry the joints, wait a few minutes, and check again. A dry joint is a good joint.

When to call a handyman

Call Richard if the pipework needs moving, the new radiator is significantly larger than the old one, or if the system loses pressure repeatedly after the swap. Persistent pressure loss usually means a leak elsewhere, which is a job for a Gas Safe engineer or a plumber. Richard will let you know honestly what the problem is.