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Curing a Noisy Central Heating System

A noisy central heating system can be very inconvenient: e.g. waking you up as it starts in the early morning; or worrying, as you start to wonder whether it is going to break down. Domestic central heating systems can emit a whole range of noises from humming and whirring, through clicking and knocking to full-blown bangs, which can be from the pipes, radiators or boiler.

Heated towel railGurgling Heating System: Watery gurgles are often caused by trapped air. To remedy this, turn off the central heating and bleed the radiators (see Bleeding Radiators Blog).

Humming Central Heating:  A humming noise is often caused by the pump. If it’s set too fast, it will cause a loud vibration, so try turning it to a lower setting. Alternatively, the pump may be causing vibration in the pipes. You can mount the pump onto brackets that absorb the vibrations. If this does not work, it may be that the pipes themselves are too small for the amount of water trying to pass through.

Knocking, Clicking or Creaking: As the water in the central heating system heats up, the pipes expand; contracting again as they cool. If there’s not enough space to allow for the pipes to expand, it will cause noises under the floorboards or in the walls. If the rubbing is occurring by the floor joists, cut a little wood away on one side. Do not cut too much or this will weaken the joist. Packing some insulation around the pipe will also prevent the rubbing noise.

If the pipes have plenty of room but are still knocking, they may lack support. Fit small wooden battens between the joists to support extra pipe clips.

A build-up of contaminants and scale in your radiators can cause hot water to release any gases it contains, making a noise as it does so. To clear out scale, drain down the system and flush it out. When you refill the system, use a rust inhibitor.

Another very common source of banging is a thermostatic radiator valve. If the noise starts after the system has been on for a while, go to each radiator and adjust the temperature up or down. If the noise stops, it is likely that the valve is faulty or is incorrectly orientated.  If your thermostatic valve is the wrong way round, water is flowing through it in the wrong direction, which causes banging when the valve is opening or closing.

Banging or Hammering Loud banging or hammering noises in the central heating system can be caused by air trapped somewhere. As well as being noisy, trapped air can lead to corrosion of radiators and the boiler. To prevent this, bleed the radiators and make sure that any vents are working properly.

Trapped air in the boiler can also cause loud banging noises; or, a build-up of sludge and scale could be causing steam pockets within the unit. Sludge inhibits water flow so, as the water tries to force its way through, it causes noise. To clear the debris, add a non-acidic cleaner and descaler into the feed/expansion tank and drain a few days later.

The boiler may be noisy because it is straining owing to lack of water flow. Examine the feed/expansion tank to make sure that it’s topping up when the ball cock opens. If it isn’t, it may be that the mains supply is switched off, the ball cock is seized, there’s an air lock, or there’s a frozen pipe.

If the boiler thermostat is set too high or is faulty, the water temperature will be too high, which can also cause noise. You can test this by turning down the boiler thermostat (not the room thermostat).

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