Makes we repair
What a boiler making a noise is telling you
A new noise from a boiler, louder than its usual whirr, is a sign of a change inside it or in the heating around it. Some sounds are normal, as the makers' guides describe them:
- a faint whirring while the heating or the hot water runs
- the boiler lighting, and its pump moving the water
- the fan running on for a while after the burner stops
Louder, unfamiliar noises are a sign of a problem. Each sound points to its own causes:
- Gurgling is air in the system, or in a frost a frozen condensate pipe.
- Whistling and banging are signs of kettling, where the water boils inside the boiler.
- Humming and droning point to the water pressure, the pump or the fan.
You can check some of these causes yourself, safely, while the rest are an engineer's. Every boiler problem, and what each usually means.
Sources: Glow-worm's and Vaillant's advice on boiler noises, and Ideal's boiler FAQs.
The sounds, one by one
The sounds below are the ones Vaillant's and Glow-worm's own guides describe, with what each maker links them to. Neither maker ranks the causes by how often they happen, so the list keeps their order.
Gurgling
What the makers link it to
Air trapped in the system, or in a frost, a frozen or blocked condensate pipe.
The first step
Bleed the radiators. In a frost, look at the condensate pipe.
Whistling, like a kettle
What the makers link it to
Kettling, where water boils inside the boiler from limescale, a faulty thermostat or a damaged pump. In a soft water area, it can be air.
The first step
Ring us.
Banging or knocking
What the makers link it to
Kettling, a faulty pump or sensor, or a loose pipe moving as the water runs.
The first step
Look at the pipes you can reach, then ring us.
Humming
What the makers link it to
Mains water arriving at too high a pressure, the pump sending water round too fast, or the fan.
The first step
Ring us.
A drone, like an aeroplane
Whooshing
What the makers link it to
A blocked air intake pipe, or a blocked air filter inside the boiler.
The first step
Ring us.
A loud vibration
What the makers link it to
A damaged pump or a blocked flue, sometimes with the pressure out of range.
The first step
Read the pressure gauge, then ring us.
Sources: Vaillant's and Glow-worm's advice on boiler noises, Glow-worm's advice on a boiler that keeps turning off, and the condensate pipe advice of Worcester Bosch, Baxi and Ideal.
What you can safely check
A householder's checks for a noisy boiler come from the makers' own guides. Never unscrew the boiler's case, and never touch anything that carries gas.
1. Bleed the radiators
Bleeding the radiators lets out trapped air, the cause of gurgling. Turn the heating off and let the radiators cool for about an hour. The bleed valve sits at the top of each radiator, at one end. Hold a cloth beneath it, and open it a quarter to half a turn with a radiator key. Close it again once water follows the hiss. Glow-worm suggests starting downstairs, as air rises. Radiators cold at the top, and bleeding them step by step.
2. Check the pressure afterwards
The pressure gauge drops as you bleed. Read it with the heating off and the boiler cool. Vaillant and Glow-worm ask for 1 to 1.5 bar. If it reads low, top up the pressure the way your user guide shows. Glow-worm adds that a boiler making a loud vibrating noise may show the pressure out of range. When it does, the two are likely linked, so ring us.
3. In a frost, look at the condensate pipe
The condensate pipe is the white plastic pipe from the boiler to a drain outside. In a hard frost it can freeze and make the boiler gurgle. Where it is frozen at ground level and you feel able, warm it with warm water, never boiling, or a hot water bottle. Then restart the boiler as its guide shows. A pipe frozen high up a wall is one to ring us about.
4. Look, without touching
The pipes you can reach are worth a look for one that moves or knocks as the water runs. Outside, look at the flue's end for an obvious blockage such as leaves, without touching it. If something is there, ring us.
If these checks don't quiet the boiler, stop there. We'll ask you to describe the noise when you ring.
Sources: Glow-worm's and Vaillant's bleeding guides and their advice on boiler noises, and the condensate pipe advice of Worcester Bosch, Baxi and Ideal.
When a noise needs an engineer
A noisy boiler needs an engineer once bleeding the radiators hasn't stopped the noise. Some sounds need one straight away:
- A whistle like a kettle, or banging. Vaillant says kettling can be dangerous and should be inspected by a Gas Safe engineer.
- Loud banging or clunking. Glow-worm says to call a registered engineer as quickly as possible.
- A drone like an aeroplane, or a hum that won't stop. The makers point to the pump or the fan, inside the case.
- A whoosh, or a loud vibration. Either can mean a blocked air intake, filter or flue, or a damaged pump.
- A gurgle that comes back after bleeding, or comes with the boiler locking out.
- A noise with a code on the display, or water around the boiler.
If you smell gas, leave the boiler alone. The free emergency number is in the gold "Smell gas?" bar on this page. Gas safety at home, and what to do about a gas smell. Otherwise, ring us and describe the noise, as finding its cause is our Gas Safe registered engineers' job. What a repair visit involves, from the first checks to the fix. Water around the boiler, and what a leak under or near it usually means.
Worth knowing
Glow-worm suggests bleeding your radiators about once a year, and raising it at the boiler's service if you find you keep needing to.
What changes the price of the fix?
The cost of fixing a noisy boiler depends on what is making the noise. Letting the air out of the radiators may need no part at all. A pump, a sensor or a thermostat is a part to fit, and limescale or sludge means cleaning the system. The rate is agreed when you ring, before an engineer sets off, and no work is done until you say yes. How our rates work is set out in full.
Do you cover my part of London?
Yes: we fix noisy boilers all over Greater London, day and night, in every borough north and south of the Thames. Pick your side of the river to see the areas.
North of the river
Every borough north of the Thames: Barnet and Enfield at the top, Hillingdon in the west, Havering in the east, and central London in between.
South of the river
Every borough south of the Thames: Richmond and Kingston in the west, Bexley in the east, and down through Croydon to Sutton and Bromley.
Questions about boiler noises
Is a noisy boiler dangerous?
A noisy boiler is usually not an immediate danger, Vaillant and Glow-worm say. Boilers are built to shut down before a fault turns dangerous, though Vaillant adds that this isn't guaranteed. Kettling is the noise Vaillant singles out as one that can be dangerous. Either way, a new noise should be looked at soon, so ring us. If you smell gas, open the gold "Smell gas?" bar on this page for the free number.
Does limescale make a boiler noisy?
Limescale can make a boiler noisy. Vaillant and Glow-worm both name limescale in the heat exchanger as a cause of kettling. A build-up is most likely in a hard water area. Hard water, limescale and the yearly service.
Could the noise be the radiators, not the boiler?
The radiators and their pipes can make noises of their own. Clanking or rumbling as the heating warms up is air in the radiators, Glow-worm says. A bang can be a loose pipe moving as the water runs. Air in the radiators, and how to bleed it.
How much does it cost to fix?
The cost of fixing a noisy boiler depends on what is making the noise, and the part it needs, if any. The rate is agreed with you on the call, before an engineer is on the way. How our rates work is set out in full.
Don't know what has failed? You don't have to.Ring and say what you can see or hear. Finding the fault is our job.
Calls answered 24 hours a day
A real person answers and gives you the rate on the call. No work starts until you say yes, and repairs are guaranteed for 12 months: parts, labour and any return visit.
