Replacing a radiator on an existing UK heating circuit

Swapping one radiator for another of the same size is one of the more approachable heating jobs. The pipes stay where they are, the valves stay where they are, and you are only draining the water in one radiator. It gets harder fast when anything is different: the new radiator has different pipe centres, a valve will not shut, or a joint starts to weep. This guide covers the like-for-like swap and where to stop.

It deals only with the radiator and its two valves. It does not cover the boiler, the gas supply or anything inside the boiler casing. For that, see when to call a Gas Safe engineer.

Before you start: is it really like-for-like?

Measure the old radiator before you buy. The number that matters most is the pipe centres: the distance between the centre of one valve tail and the other, measured along the wall. Also note:

• the height and length of the radiator;
• whether the pipes come up from the floor or out of the wall;
• whether the valves connect to the bottom of the radiator at each end (the most common UK arrangement) or somewhere else;
• the type of radiator, such as single panel or double panel with fins.

If the new radiator has the same centres and the same connection positions, the existing valves will usually line up and the job is a swap. If the centres differ, the pipes have to be moved or extended, which is a different job. See "When it is not like-for-like" below.

Also check that the new radiator gives enough heat for the room. A bigger or smaller radiator in the same space changes how warm the room gets. Our radiator sizing guide explains how output is described.

What you will need

• Two old towels and a shallow tray or a roasting tin that fits under the valve.
• A bucket and some containers for the water.
• Two adjustable spanners or grips: one to hold the valve body, one to turn the union nut.
• A radiator bleed key.
• A lockshield key or small spanner, if the lockshield has no cap you can turn by hand.
• Thread sealing tape or the sealant the radiator maker specifies for the tails and the vent.
• Dust sheets. Heating water is black and stains carpet.

Taking the old radiator off

1. Turn the heating off and let it cool. Never drain a hot radiator.
2. Close the valve at one end. On a thermostatic radiator valve, turn the head to its lowest setting. Many TRV heads do not fully close the valve, so if yours has a manual cap or decorator cap, fit that and screw it down. Our guide to radiator valves and TRVs explains the types.
3. Close the lockshield at the other end, counting the turns. Write the number down. When you open it again by the same number of turns, the radiator stays roughly balanced with the rest of the house.
4. Put the tray and towels under one valve. Hold the valve body still with one spanner and slowly loosen the union nut between the valve and the radiator with the other.
5. Open the bleed valve a little at the top of the radiator to let air in. Water will start to run from the loosened union. Control the flow with the union nut and empty the tray into the bucket as you go.
6. When it stops, undo the union at the other end and drain what is left.
7. Lift the radiator up and off its brackets while keeping it level. Then tip it to drain the last of the water into the tray. Radiators are heavier and dirtier than they look, so have help for anything large.

Keep watching both valves after the radiator is off. If either is still dripping, the valve is not closing fully. Stop and read the section below.

Hanging the new radiator

1. Check the brackets. If the new radiator is the same make and size, the old brackets may fit. Often they do not, and new brackets come in the box. Mark and fix them so the radiator sits level, or very slightly higher at the bleed valve end.
2. Fit the tails and the bleed vent and blanking plug into the new radiator, sealing the threads as the maker says.
3. Hang the radiator and line the tails up with the valves. Do not force a valve sideways to meet a tail. If they do not meet comfortably, the centres are wrong.
4. Tighten the union nuts while holding the valve body still.
5. Open the lockshield by the number of turns you wrote down, then open the other valve.
6. Bleed the new radiator until water comes out of the vent. See bleeding and balancing radiators.
7. Check every joint with dry tissue for the next few hours and again after the heating has run.

Refilling the system

Draining one radiator takes water out of the heating circuit. What happens next depends on your system:

• Open-vented system (a small feed and expansion tank in the loft): the tank refills automatically.
• Sealed system (usually a combi or system boiler with a pressure gauge): the pressure will have dropped. See our guide to checking boiler pressure. If you are not sure how to restore it, or you cannot find the filling point, call a Gas Safe registered engineer or a heating plumber.

Any water you add dilutes the corrosion inhibitor in the system. If you have drained more than a little, read about inhibitor and sludge and ask a plumber whether it needs topping up.

When it is not like-for-like

Stop and call a plumber if:

• the pipe centres are different and the pipes would need moving, extending or bending;
• a valve will not close, or keeps dripping when it should be shut. The fix usually means draining more of the system;
• a tail or union leaks after you have tightened it once. Overtightening can split an olive or crack a valve body;
• the pipework is plastic and you are not sure how the joints were made, or the pipes are the thin microbore type and kink easily;
• the radiator is on the same circuit as a towel rail with an electric element. See towel rails.

If the boiler shows a fault, will not restart, or the pressure keeps falling after the job, stop. That is a job for a Gas Safe registered engineer. Our guide to hiring a plumber covers finding the right trade.

Products at Wickes and Amazon

We haven't tested these. They are examples, with what the retailer's page says.

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

Can I replace a radiator without draining the whole system?

Usually yes, if both valves close fully. You drain only the radiator you are removing. If a valve will not shut off, more of the system has to be drained, and that is a plumber's job.

Why has my boiler pressure dropped after changing a radiator?

On a sealed system, the water you drained came out of the heating circuit, so the pressure falls. Read the boiler maker's instructions or our boiler pressure guide. Call an engineer if you cannot restore it safely.