Gas Safe registered 25 years in the trade 12 years running the business
Written by Chris Gill, C Gill & Son Plumbing & Heating ·
Gurgling
A gurgle usually means air or gas bubbles moving through the water in the system. Air collects in radiators and pipes over time, and you may hear it most when the heating first switches on. Low system pressure can make it worse, so check the gauge on a combi or system boiler.
In freezing weather, gurgling can come from the condensate pipe, the plastic pipe running outside to a drain. When it starts to freeze, water backs up and gurgles before the boiler locks out. Pouring warm, not boiling, water along the outside section usually clears it.
Banging or kettling
A rumbling or banging noise, a bit like a kettle coming to the boil, is often called kettling. It tends to happen when limescale or sludge builds up on the heat exchanger inside the boiler. Water gets trapped against the hot surface, overheats and forms steam bubbles that collapse with a bang.
Kettling is a sign the boiler is struggling to pass heat into the water properly. It does not fix itself, and it is something to get looked at rather than live with.
Whistling and humming
A high whistle often points to restricted flow: something is stopping water moving freely through the boiler, so it heats up too quickly in one spot. That could be sludge, a partly closed valve or a pump that is not doing its job.
A low hum or drone usually comes from the pump or a vibrating pipe. Sometimes the pump is simply set higher than it needs to be; sometimes it is wearing out. Pressure that is too high or too low can also change the sound the system makes.
Clicking without firing
A few clicks as the boiler starts are normal. Repeated clicking with no burner lighting is different. It usually means the boiler is trying to ignite and failing, which can be down to the ignition electrode, the gas supply or a fault the boiler has detected.
This is one to leave alone apart from checking the display for a code and making sure other gas appliances are working. Anything to do with ignition or gas parts has to be handled by a Gas Safe registered engineer.
Is it the boiler or the radiators?
Not every noise comes from the boiler. Ticking pipes as they warm and cool, a radiator that gurgles or a valve that hums can all sound like boiler trouble from another room. Stand near the boiler while the heating starts, then walk round the radiators.
If a radiator gurgles and is cold at the top, bleeding it may help; our guide to a radiator cold at the bottom or top explains how to bleed it safely. Noisy pipework and system-wide circulation problems come under our central heating work.
When a service helps and when a repair is needed
Some noises are picked up and sorted during a yearly boiler service, especially early signs of sludge, a blocked condensate trap or pressure set wrong. A service is also when an engineer can listen to the boiler running and spot a part that is starting to wear.
Other sounds, such as persistent kettling, clicking without lighting or a failing pump, need a repair visit. If the boiler is older and has started making noises alongside other problems, our guide on how long a boiler lasts helps you weigh up repair against replacement.
Book a visit
Call or WhatsApp 07429 632804 and describe the noise, when it happens and any code on the display. A short video recorded on your phone while the boiler makes the sound is really useful. Chris is Gas Safe registered with 25 years in the trade, and you can read more about our boiler repairs. If you smell gas at any point, call 0800 111 999 first.
Common questions
Noisy boiler FAQs
Clear answers before you arrange a visit.
Is a banging boiler dangerous?+
It is usually a sign of limescale or sludge rather than an immediate danger, but the boiler is under strain. Switch it off if the banging is severe and get it checked.
Why does my boiler gurgle when the heating comes on?+
Most often it is air in the system or low pressure. In freezing weather, check whether the condensate pipe outside has started to freeze.
Can bleeding radiators stop the noise?+
If the noise is air in the radiators, yes. Check and top up the boiler pressure afterwards, as bleeding lets a little water out.
Will a service fix a noisy boiler?+
Sometimes. A service can sort settings, a blocked condensate trap or pressure issues, but worn parts or heavy sludge need a separate repair.
Does a noisy boiler mean it needs replacing?+
Not usually. Most noises come from a fixable cause. Replacement only comes into it if the boiler is older and unreliable in other ways too.
