Ensuring that your heating is working efficiently is a must – not only for your own comfort, but for your bank balance. During the colder months, you need your whole property to warm quickly and stay that way, and 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.
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.
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.
Never bleed your radiators when they're hot otherwise scalding water could be released.
You will need:
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.
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.
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.
Hot pipes expanding and rubbing against the floor, wall or other pipes.
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.
It could be that the pump speed is too high or that your pipes are too narrow for the system flow.
Call an engineer.
Air or gas bubbles in the system.
Bleed the radiators (see How to bleed a radiator) and if the problem persists, call an engineer.
Faulty boiler thermostat.
Call an engineer to check.
Limescale build-up. Hard water areas can have a lot of limescale build up in the system and this could be causing the noises.
Call an engineer to clean it out. They may decide that it’s worth fitting a hard water filter to stop it happening again.
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.Shop central heating cleansers Shop central heating protectors
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.
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.
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.Shop noise reducers
The water level in the system is too low.
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.
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.
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.
Your pump isn’t working.
See Hissing and/or banging noises.
Your pump’s thermostat or timer is incorrectly set or faulty.
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.
Your zone valve’s thermostat or timer is incorrectly set or faulty.
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.
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.
Call an engineer to ‘balance the system’.
The zone valve itself may be faulty.
Replace the zone valve with a new one.
The radiator’s manual control valve is turned off.
Open/ turn on the valve.
The thermostatic radiator valve (TRV) could be incorrectly set.
The TRV might be faulty.
Replace the TRV with a new one.
You may have an incorrectly set lockshield valve.
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.
Heavy corrosion deposits may be blocking the inlet and outlet.
Remove the radiator and flush it out or replace it if needs be. Be sure to add corrosion inhibitor to the system.
Air trapped inside.
Open the bleed valve so that it can escape (see How to bleed a radiator), and if the problem persists, call an engineer.
A build-up of sludge. Sludge is produced by air, water and metal mixing. Corrosion could also be restricting the water flow.
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).