Radiator Repair

Where a radiator is cold tells you most about the cause:

Sludge is black, magnetic sediment from corrosion inside the system. One affected radiator can sometimes be removed and flushed out on its own. If several are cold at the bottom, power flushing cleans the whole system, and a magnetic filter helps stop it coming back.

If the whole house is cold and the boiler has stopped, the fault is not the radiators: see our boiler repair service.

Bleeding lets out trapped air. It is a job you can usually do yourself:

1. 1

   Turn the heating off and let the radiators cool.

2. 2

   Find the bleed valve, a small square screw at one top corner, and hold a cloth under it.

3. 3

   Open it a quarter turn anticlockwise with a radiator key. You will hear air hiss out.

4. 4

   Close it as soon as water starts to come out.

5. 5

   Check the boiler pressure gauge. On a sealed system, bleeding lowers the pressure. Typically it should read around 1 to 1.5 bar when cold; if it has dropped, top it up using the filling loop as the boiler manual explains.

If a radiator needs bleeding every week or two, air or gas is getting in, often from a small leak, a faulty automatic air vent or corrosion. That needs finding, not repeated bleeding.

Most radiator leaks come from the valves and joints, not the radiator itself:

• Valve spindle (gland): Water around the spindle under the head or cap. Often cured by gently tightening the gland nut or repacking the gland; if not, the valve is replaced.
• Compression joints: Where the valve meets the pipe. The nut may need tightening, or the olive replaced.
• Valve tail: The threaded connection into the radiator. Resealed or replaced.
• Bleed valve: A worn bleed screw can weep. It is cheap to replace.
• The radiator body: Pinhole leaks or rust along the bottom seam mean the radiator is corroding from the inside. It cannot be repaired properly and needs replacing through our radiator installation and replacement service.

Leak sealer products added to the heating water are not a reliable repair. If you have damp patches but no visible drip, the leak may be under the floor: our leak detection and pipe repairs service can trace it.

If the radiators nearest the boiler are hot and those furthest away are lukewarm, the system needs balancing: the water takes the easiest route, so nearby radiators take more than their share.

Balancing is done with the lockshield valve at the opposite end to the TRV. The radiators furthest from the boiler are left more open, and those closest are turned down, until each radiator heats up evenly. A professional balance measures the temperature of the flow and return pipes at each radiator, so every radiator gives similar output. It is worth doing after a radiator is replaced, moved or added, or after a power flush.

• Gurgling or trickling: Air in the radiator or pipes. Bleeding usually cures it.
• Ticking or creaking as it warms: The radiator or pipes expanding against brackets, floorboards or notches in joists. Repositioning clips or pipe supports helps.
• Whistling at the valve: Water forced through a nearly closed valve. Rebalancing usually helps.
• Banging or kettling from the boiler: A system or boiler problem, often scale or sludge, which needs a whole-system check.