You shouldn’t be surprised by all boiler sounds. Quiet whirring, deep rumbling, or the occasional quiet clicking sound are the acceptable. But any other sounds warrant an investigation.

In this article I’ll explain some problematic boiler noises and how to fix them. I’ve also included affiliate links to Amazon (in orange color) so you can see some replacement parts that can come in handy if your boiler is begging for a little extra love.

1. Gurgling Boiler Noises

Gurgling noises make it seem like your boiler is fastidious about oral health, gurgling mouthwash every so often. Gurgling noises are low liquid sounds that result when air passes through water.

Unsurprisingly, a boiler will produce gurgling noises if there’s air trapped somewhere. If you have central heating, the trapped air may end up in the radiator, leading to gurgling sounds when you switch it on.

Frozen discharge pipes may hinder proper water circulation in the condensate pipes leading to loud gurgling sounds. Low water pressure in the boiler may lead to gurgling noises.

How to Fix a Gurgling Boiler

• Bleed the radiator: If you suspect that there’s air trapped in the boiler lines, touch the top of the home’s highest radiator, and it’ll likely have a cold patch. Radiators come with bleed keys that you can simply turn to release the trapped air. Hot water will jet out of the bleed valve, so avoid touching it.
• Check the water pressure: Use a manometer or a pressure gauge to check the water pressure inside the boiler. Typically, the pressure gauge is in the control panel but may be located under the boiler next to the pipes. When the pressure falls below one bar, the boiler starts to gurgle. Topping up the water level solves this problem.
• Check the condensate pipe: The condensate pipe removes the excess water vapor from the boiler system. During cold weather, the water can freeze, effectively blocking the line. Use warm water to thaw the icicles on the pipe, and the gurgling noises will stop.

2. Buzzing or Whining Boiler Noises

If you notice whining or buzzing sounds coming from your boiler, you’re dealing with a delicate problem. Typically, the noises are caused by a vibrating fan bearing, worn pump bearing, or a faulty burner. These are serious problems that call for the attention of a qualified professional.

How to Fix a Buzzing Boiler

The buzzing boiler sounds are quite like vibrating or humming sounds. Start with the fixes detailed under “How to fix a vibrating boiler.”

If none of those fixes the problem, the boiler could be buzzing due to worn pump bearings, a faulty burner, or worn fan bearings. While you may replace the fan bearing and the burner, a worn pump bearing means it’s time to buy a new boiler.

3. Banging and Clanging Boiler Noises

If your boiler produces recurring banging noises, the noise could be a result of kettling. The noise sounds like a pot of popcorn on a cooktop but mostly sounds like a boiling kettle. The squealing often results from limescale buildup on the heat exchanger, restricting water flow and causing it to boil.

Despite what the name suggests, a boiler doesn’t actually boil the water; instead, it usually heats it to around the 70 °C range. The banging noises result when boiling water expands and turns into steam and is the same sound you get from a boiling kettle.

A faulty boiler thermostat or set incorrectly setup may cause the boiler to overheat the water, leading to banging noises. A loose pipe connection could also be the source of the banging noises.

How to Fix a Banging Boiler

• Check the pipe connections: Check over the pipes connected to the boiler and ensure they’re well secured in place. Retighten loose screws to keep the pipes from moving as the hot water flows through them.
• Remove the limescale buildup: Limescale is notoriously tricky to remove from a boiler. Start by flushing out your system with a good central heating inhibitor to remove most of the sludge.

Fit the system with a limescale reducer to catch any limescale passing through the system to prevent further banging and clunking noises. A powerflush is a more effective way to deal with limescale and debris buildup.

• Replace the faulty thermostat: A new thermostat with the correct setting will keep the boiler from overheating the water. That solves the banging problems and lowers your monthly heating bills.

4. Whistling Boiler Noises

If your boiler is making whistling noises, you’re likely dealing with limescale buildup in the heat exchange or your pipes. When the water is heated, the dissolved minerals in the water precipitate, forming limescale that settles at the bottom.

With time, the limescale creates a blockage in the pipes by reducing their diameter. As a result, the heat exchanger fills up with hot steaming water, leading to a pressure build-up.

The high pressure causes the steam to escape through the pressure valve, producing kettle-like whistling noises.

While a limescale buildup in a boiler is expected, it can cause extensive boiler damage if left unattended. The situation is worse in hard water areas or using well water in your home.

The buildup compromises the boiler’s efficiency and c ould saddle you with hefty heating bills each month while lowering the boiler’s lifespan. Installing a water descaler is advisable when living in a hard water region.

How to Fix a Whistling Boiler

Taking quick action can extend the lifespan of a whistling boiler and save you a great deal of money. Start by bleeding your radiators to remove air from the system.

If the banging noises continue, the banging could result from kettling, and you may need to flush the hot water system.

Flushing means replacing the old rusty water with fresh water. However, flushing won’t work if there’s considerable limescale buildup on the heat exchanger.

For that, you’ll need to perform a power flush to rid your boiler of the scale and sludge build-up.

5. Tapping Boiler Noises

You’re likely to notice the tapping noises whenever you turn on the boiler. Tapping sounds are characteristic if the boiler is overheating.

The noise could result when there’s limescale buildup or corroded debris on the surface of your heat exchanger. The buildup restricts the water to and from the heat exchanger, leading to localized boiling, and the hot water turns into steam.

How to Fix a Tapping Boiler

A boiler’s tapping noise often results from a sludge buildup in the radiator or pipes. The sounds get louder when the pump comes on and circulates the water in the central heating system.

Check if your boiler’s thermostat is functioning correctly by turning off the boiler and letting the system cool down. Once the boiler cools down, turn it on again, then turn up the thermostat. If the thermostat doesn’t click, you may need to call a gas engineer.

Sometimes the tapping noises may result from unsecured pipework moving around. The force of the hot water flowing the pipe causes them to move, resulting in persistent tapping sounds. Properly securing the lines to the walls or the floor can fix this problem.

6. Clicking Boiler Noises

A boiler is likely to produce clicking noises if it’s struggling to ignite due to various reasons, including low pressure, no gas, faulty thermocouples or valves, or dirty pilot light.

How to Fix a Clicking Boiler

Cleaning a dirty pilot light is the easiest fix. Remove the dirt and debris around the pilot light with a cloth or a wire brush. A constant drop in pressure and faulty valve could mean the boiler has sprung a leak.

Check for any signs of staining around the boilers to find the leak. If you smell gas or your monthly gas bill spikes out of the blues, you may be dealing with a gas leak.

7. Humming Boiler Noises

Loud humming noises in an electric water heater could mean there’s a loose component. The noise is likely to result if your boiler was recently installed or repaired. High water pressure in the boiler may also lead to loud humming noises.

If there’s a steam buildup, the boiler releases the excess pressure through the pressure release valve, creating a humming or whistling noise. Lastly, the humming noise could result if the circulating pump’s speed is set too high.

How to fix a Humming Boiler

Examine the boiler when it’s humming. If the unit vibrates, it’s not secured firmly to the ground. Have a technician install new boiler brackets or tighten the existing ones.

If the boiler isn’t vibrating, you’re likely dealing with loose parts. Tighten the screws holding the boiler’s panel in place. If that doesn’t work, you may need to consult a technician.

Check the boiler’s pressure gauge. The boiler is likely to hum or whistle if the pressure rises above 20 psi (pounds per square inch). The ideal setting should be 15 to 20 psi.

Lower the speed at which the water circulates between the boiler and the radiator by setting a lower speed on the circulator pump.

8. Vibrating Boiler Noises

Your boiler is likely to produce vibrating noises due to a malfunctioned boiler pump that’s moving around its casing. Or that the pump speed is set too high, causing the water to move around the hot water system too fast, creating whooshing noises and causing the boiler to vibrate.

If the pressure inside the boiler and the heating system is too high, the valves inside the system may start to hum and vibrate. Lastly, a blocked flue or air intake may lead to humming or vibrating. The air intake is on the outside, and it can be blocked by feathers, leaves, nests, and other debris.

How to Fix a Vibrating Boiler

• Check the pump: Ensure the pump is properly secured to eliminate shaking and vibrations. Also, ensure that the pump is set at the correct speed.
• Check the pressure: High pressure in the boiler often leads to humming or vibrating noise. The ideal pressure for a cold boiler is below 1.5 bar and between 1.5 and 2 bars when hot. If the cold boiler is higher than 1.5 bars, remove some water from the system to lower the pressure.
• Check the air intake: Blockages in the air intake could lead to whooshing or vibrating noises. Remove any foreign objects or fluff from the flue and ensure it’s free from obstructions. You should feel the air movement when you place your hand over the air intake.

9. Rattling Boiler Noises

If your boiler is emitting rattling noises, that could indicate the presence of loose objects or sludge in the system. The noise could also result if there’s air trapped in the pipework.

Fixing Rattling Boiler Noises

Bleeding your radiators can help remove the excess air from the system. Just make sure to re-pressurize the boiler correctly once you’re done bleeding the radiators.

If the rattling noise persists after bleeding the radiators, you could be dealing with a loose valve. Try and locate the source of the noise and tighten any loose valves you encounter.

Check if there are any unclipped pipes since they also produce rattling noises. If the radiator valve and the lines are in order, but the noise persists, you could be looking at a faulty boiler pump or valve.

How to Do a Powerflush

A standard flush is insufficient when dealing with noises caused by debris or limescale buildup in your boiler. A powerflush or a chemical clean that rids your boiler of these buildups.

A powerflush entails attaching specialty equipment to your heating system and using it to flush out the accumulated debris. The machine pumps water and cleaning chemicals into your hot water system to dislodge the debris.

Once the system is thoroughly cleaned, you need to add a central heating inhibitor. The inhibitor keeps sludge from accumulating inside the boilers.

However, if your home has a microbore pipe central system, you’re better off with a chemical clean instead of a powerflush. A chemical cleanse entails pouring a chemical inside your hot water system to dissolve the limescale and other debris.

Leave the chemical to sit in your hot water system for two weeks. Drain the system after two weeks and refill it with fresh, clean water mixed with a central heating inhibitor. As the name suggests, the inhibitor protects your boiler against future debris buildups.

Alternatively, you may choose to install a magnetic filter in your hot water system to catch the debris before it gets to your central heating system.

You’re likely to notice a noise reduction, improved operational efficiency, and lowered heating bills after a chemical clean or a powerflush.

Bottom Line

While annoying, boiler noises are sure indicators that your boiler is in dire need of repair and maintenance. The sooner you attend to this problem, the sooner you can enjoy your beauty sleep instead of losing sleep over the astronomical boiler replacement costs.