How to fix problems with radiators

Help to maintain the radiators in your home

Ensuring that your heating is working efficiently is a must – not only for your comfort, but for your bank balance. During the colder months, you need your whole property to warm quickly and stay that way. Knowing how to fix any minor issues yourself will help your home stay warm, without you having to fork out for an engineer.

While you need a qualified professional to install a central heating system, maintaining them isn’t difficult and most tasks take no time at all to complete. So you’ll only need to call in the experts if something isn’t easily fixed and we’ll help you understand if and when you need to make that call.

As well as teaching you about how your system works, we’ll show you how to bleed your radiator and tackle faults like noisy or cold systems.

Help to maintain the radiators in your homeHelp to maintain the radiators in your homeHelp to maintain the radiators in your homeHelp to maintain the radiators in your home

In a wet central heating system, a boiler heats water before it’s pumped around a circuit of pipes to radiators fitted throughout the house. Each radiator has valves that control the rate at which water flows through it, therefore controlling the amount of time the water spends in the radiator and the amount of heat that is given off. When the water leaves the radiator, it’s piped back to the boiler for reheating.

Some heat is lost from the pipes as the water flows around the system, but this is kept to a minimum by the pipes being very narrow as well as the speed at which the water travels. A well-designed system may have several short circuits radiating from the pump, rather than one large one, to make sure that the last radiator on each circuit heats up just as efficiently as the first.

How a radiator worksHow a radiator worksHow a radiator worksHow a radiator works

Keeping your radiators well-maintained will save energy as they’ll function more efficiently. If your radiator is cold at the top but hot at the bottom, that means there's air in the system and you'll need to bleed your radiators.

How to bleed a radiatorHow to bleed a radiatorHow to bleed a radiatorHow to bleed a radiator

Before you begin

Never bleed your radiators when they're hot otherwise scalding water could be released.

You will need:

How to bleed a radiator Step 1How to bleed a radiator Step 1How to bleed a radiator Step 1How to bleed a radiator Step 1

Step 1

Turn off your central heating and allow the radiators to cool. Work on the downstairs radiators first, starting at the first radiator on the circuit.

How to bleed a radiator Step 2How to bleed a radiator Step 2How to bleed a radiator Step 2How to bleed a radiator Step 2

Step 2

All radiators are provided with a bleed valve in one top corner to allow trapped air to be released. It’s a square shaft inside a threaded plug (a round hole with a square inside it). Use a radiator bleed key (or in some cases a flat-head screwdriver) to turn the shaft anti-clockwise to open the valve. This should be between a quarter turn and a half-turn – don’t unscrew it by more than one complete turn.

How to bleed a radiator Step 3How to bleed a radiator Step 3How to bleed a radiator Step 3How to bleed a radiator Step 3

Step 3

You’ll hear the trapped air hissing as it escapes. Hold a cloth beneath the valve to catch any water, and as soon as the first trickle appears close the valve by turning the bleed key clockwise.

Check all of your radiators as you may need to bleed more than one. Work on the downstairs radiators first and then move on to the ones upstairs and bleed them one at a time as required.

Turn your system back on and re-pressurise the boiler if required, the manufacturer’s manual should explain how to do this. Your radiators should now work more efficiently. If you find you have to bleed your radiators frequently, have the system checked by a heating engineer, as there is likely to be a fault somewhere that is allowing air to enter the system.



Different makes and models of boiler have different controls, so be sure to keep your boiler operating instructions in a handy place in case of trouble. Many faults have simple solutions, which you should be able to do yourself – but if in doubt, call in an engineer.

How to fix creaking pipes

Possible cause

Hot pipes expanding and rubbing against the floor, wall or other pipes.

What’s the solution?

Widen pipe notches in joists (but don’t deepen them, as this will weaken the joists), clip unsupported pipes or pack insulation around and between pipes.

How to fix humming sounds in pipes

Possible cause

It could be that the pump speed is too high or that your pipes are too narrow for the system flow.

What’s the solution?

Call an engineer.

How to fix rushing sounds in pipes

Possible cause

Air or gas bubbles in the system.

What’s the solution?

Bleed the radiators (see How to bleed a radiator) and if the problem persists, call an engineer.

How to fix rushing sounds in pipesHow to fix rushing sounds in pipesHow to fix rushing sounds in pipesHow to fix rushing sounds in pipes

How to fix hissing and/or banging noises

Possible cause 1

Faulty boiler thermostat.

What’s the solution?

Call an engineer to check.

Possible cause 2

Limescale build-up. Hard water areas can have a lot of limescale build up in the system and this could be causing the noises.

What’s the solution?

Call an engineer to clean it out. They may decide that it’s worth fitting a hard water filter to stop it happening again.

Top tip - Protect your system

For long-term protection against corrosion and limescale build up, we recommend systems are cleansed using a central heating cleaner and then protected with a central heating protector.

How to fix hissing and/or banging noisesHow to fix hissing and/or banging noisesHow to fix hissing and/or banging noisesHow to fix hissing and/or banging noises

Possible cause 3

In a solid-fuel system (where a fuel such as wood is used to heat the system), noises could indicate that the pump isn’t working.

What’s the solution?

You can check this using the boiler operating instructions. Shut down the boiler; check that the pump is turned on and the impeller running by feeling the casing for vibration. If the switch is set to on, but the pump is not running, turn off the power at the mains and check that none of the wiring connections have come loose. If the pump is running, but the outlet pipe is cool, open the bleed valve to release trapped air. If the problem persists, call an engineer.

Top tip - Use a boiler noise reducer

Adding a boiler noise reducer can help manage the noise. For open vented systems add via the head tank: if you have a sealed system add it via the radiator using an injector.

Possible cause 4

The water level in the system is too low.

How to fix hissing and/or banging noisesHow to fix hissing and/or banging noisesHow to fix hissing and/or banging noisesHow to fix hissing and/or banging noises

What’s the solution?

Step 1

Turn off the boiler and pump, and examine the feed-and-expansion cistern in the loft; if it’s empty, check that the ball valve isn’t jammed closed, that the water supply hasn’t been turned off or a supply pipe frozen.

Step 2

If you can identify and fix the cause yourself, you can then top up the system water level again, but do be sure to follow the boiler operating instructions. If you can’t find the fault, call an engineer.

Step 3

Some ball valves are adjusted simply by bending the metal float arm; others have an adjuster screw and locknut. Some have floats that can be repositioned vertically. Make sure that the float is set so that the water level is about 25millimetres (mm) below the overflow outlet.


If your boiler is still running properly but you are experiencing problems with cold radiators, there could be a number of reasons why.

How to fix your radiators when they’re all cold

Possible cause 1

Your pump isn’t working.

What’s the solution?

See Hissing and/or banging noises.

Possible cause 2

Your pump’s thermostat or timer is incorrectly set or faulty.

What’s the solution?

Check and reset if necessary. If the thermostat or timer is set correctly, turn off the power and check the wiring connections, making sure to follow the operating instructions. If the problem persists, call an engineer.

How to fix your radiators when they’re all coldHow to fix your radiators when they’re all coldHow to fix your radiators when they’re all coldHow to fix your radiators when they’re all cold

How to fix your radiators when some of them are cold

Possible cause 1

Your zone valve’s thermostat or timer is incorrectly set or faulty.

What’s the solution?

Reset it. If set correctly, switch off the power and check the wiring connections, using the operating instructions. If the problem persists, call an engineer.

Possible cause 2

The system might be ‘unbalanced’ and need ‘balancing’. Balancing is when all the radiator valves are adjusted to make sure that all the radiators heat up at the same time.

What’s the solution?

Call an engineer to ‘balance the system’.

Possible cause 3

The zone valve itself may be faulty.

What’s the solution?

Replace the zone valve with a new one.

How to fix your radiators when some of them are coldHow to fix your radiators when some of them are coldHow to fix your radiators when some of them are coldHow to fix your radiators when some of them are cold

How to fix a single cold radiator

Possible cause 1

The radiator’s manual control valve is turned off.

What’s the solution?

Open/ turn on the valve.

Possible cause 2

The thermostatic radiator valve (TRV) could be incorrectly set.

What’s the solution?

Reset it.

Possible cause 3

The TRV might be faulty.

What’s the solution?

Replace the TRV with a new one.

How to fix a single cold radiatorHow to fix a single cold radiatorHow to fix a single cold radiatorHow to fix a single cold radiator

Possible cause 4

You may have an incorrectly set lockshield valve.

What’s the solution?

Open the manual valve fully, then remove the plastic cap from the lockshield valve and use an adjustable wrench to open the valve until the radiator warms up. Next time you have the system serviced, ask the engineer to balance the radiator.

Possible cause 5

Heavy corrosion deposits may be blocking the inlet and outlet.

What’s the solution?

Remove the radiator and flush it out or replace it if needs be. Be sure to add corrosion inhibitor to the system.

How to fix a radiator with a cold top

Possible cause

Air trapped inside.

What’s the solution?

Open the bleed valve so that it can escape (see How to bleed a radiator), and if the problem persists, call an engineer.

How to fix a radiator with a cold centre and/or bottom

Possible cause

A build-up of sludge. Sludge is produced by air, water and metal mixing. Corrosion could also be restricting the water flow.

What’s the solution?

Remove the radiator and flush it out, or replace it if needs be. Be sure to add corrosion inhibitor to the system (see Adding corrosion inhibitor).

How to fix a radiator with a cold centre and/or bottomHow to fix a radiator with a cold centre and/or bottomHow to fix a radiator with a cold centre and/or bottomHow to fix a radiator with a cold centre and/or bottom