Why is my boiler making a noise?

A boiler should run smoothly and relatively quietly. You may never hear your boiler at all, especially if it's hidden away in a compartment or garage, but if yours is exposed, some sounds are normal and some will require expert investigation.

In this article, we look at both kinds, so you can judge whether to call an engineer. However, if you’re in any doubt, we’d always recommend making that call just in case. Fixing a noisy boiler can be easily affordable and effective – ignoring it could be expensive or even dangerous.

Normal sounds your boiler should make

Just like a car or even a laptop, your boiler contains moving parts, and inevitably, they’re going to create noise. Boilers are doing some pretty hard work when they’re on – heating water and pumping it around is quite intense, so you shouldn’t be surprised that sounds come from within it.

If you get a new boiler, the engineer will test it, so listen to the sounds it makes and ask any questions about where they’re coming from. That way, you’ll better identify anything abnormal.

Why is my boiler making a quiet whirring sound?

If the heating is on, it’s normal to hear a quiet whirring. This is the pump circulating water around the boiler’s burner and heat exchanger, and possibly pumping your hot water to the radiators.

Why is my boiler making a deep rumbling sound? 

When you turn on your gas boiler, the flames ignite and start vigorously boiling the water passing over them. Although it should be quiet, it might still be audible, just as you can hear your gas burner on your cooker hob.

Why is my boiler clicking?

Modern boilers have information coming from thermostats and the control panel, and this triggers switches and valves inside the boiler as components are switched on and off and water is redirected. Although they are usually silent, you might hear them from time to time. 

Boiler noises that require investigation

Once you’ve got used to the sounds your boiler makes in normal operation, you’ll notice straight away if it’s behaving unusually. Below we’ve listed the most common sounds to listen out for.

Why is my boiler banging? 

More often than not, a banging noise from your boiler is traced back to a process called kettling. This is usually when limescale builds up on the heat exchanger and restricts the flow of water to the point where it literally boils. (Contrary to the name, boilers shouldn’t actually boil water to 100°C – it’s usually in the 65–70°C range.) The banging sound you hear is the water turning to steam and expanding, just like the sound you get from a kettle.

In the absence of limescale, it’s possible that you have a faulty boiler thermostat (not the room thermostat), or one that’s set up incorrectly so it’s overheating the water.

Banging boiler pipes

What if the banging noise is coming from the pipes rather than the boiler itself? This often indicates hammering from a reversal of water flow in your pipes, such as when you turn your taps or shower on or off. While common, hard, aggressive or frequent hammering can cause damage, so call an engineer if you’re concerned. 

Why is my boiler whistling? 

While kettling can cause a whistling sound (think of the old whistling kettles), it’s more likely that whistling is caused by trapped air in the system. It’s a relatively quick process for an engineer to release the air, but a good engineer will want to know how air is getting into the system, as that’s not normal.

Mechanical devices can’t be ruled out, either. Pumps that need oiling are prone to a squeaking or whistling sound. Again, leave it to your engineer to fix.

Why is my boiler gurgling? 

If you’ve ever gurgled mouthwash or emptied a bath, you’ll recognise this sound – a rapid, low, liquid sound caused by water being agitated and having air passed through it. So it will come as no surprise that the gurgling from your boiler is probably caused by trapped air. This air can end up finding its way into radiators too, and most people with central heating will have experienced that sound when they’ve switched theirs on. 

You can bleed your radiators as a first step. If this doesn’t work, it’s time to call in a professional – you might need to drain your whole system.

It’s also possible that your condensation pipe is frozen, which can happen in cold weather when it’s outside. This causes a blockage which stops proper circulation through the condenser. Again, you might be able to sort this out yourself by warming up the condenser pipe. Hot water bottles will do the trick. To prevent freezing in the future, consider insulating the pipe or see our guide to preparing your boiler for winter. 

Why is my boiler making a grinding noise? 

A loud grinding noise will almost certainly be caused by a faulty pump. It’s vital that you switch off your system and call an engineer, as a boiler without a pump is useless and could even overheat.

Why is my boiler making a loud vibrating noise?

Boiler vibrations can be particularly concerning, as they’re not only heard but sometimes also felt in the walls of your home.

One common cause is an unbalanced system, which leads to an uneven water flow and pressure differences. Rebalance by bleeding your radiators and adjusting your valves.

Loose parts, such as screws, in your boiler can also vibrate. A technician should check for and tighten these, although if parts are frequently coming loose, this is a clear sign that your boiler should be replaced. 

Vibration can also be caused by a thermostat malfunction, causing it to misread temperature. Replacing the thermostat can fix this. 

Lastly, build up of debris in the heat exchanger can cause your boiler to vibrate by restricting the water flow, which leads to uneven boiling. This can be fixed by a technician taking the boiler apart for thorough cleaning and then reassembling it. 

What to do if your boiler is making a noise

In all the cases above, we’ve offered a few typical causes and some possible remedies, but any action by you should be a preliminary one just to rule out other causes. If you are in any doubt whatsoever about the cause of your boiler’s noises, please get in touch with a Gas Safe engineer: Contact us.

The importance of boiler servicing

Many of the issues that cause noises can be prevented by ensuring your annual boiler service is carried out. Your engineer will identify any worn-out parts and replace the ones that have a limited lifespan, as well as checking for potential wear and tear.

Your boiler is too important to go without, but keeping it working is a matter of safety as well as comfort. Keep it checked, use it as the manual instructs and get help if you hear any unusual noises coming from it.

For more advice on boiler maintenance and more, see our tips and advice page.