Why are my Pipes Banging When Boiler Comes On?

Noisy central heating systems can be frustrating - and are usually down to pipework being badly secured, air in the system, an overheating thermostat or a limescale build-up. Here we'll explain some of the typical causes for pipes banging when you turn your boiler on and the steps required to fix the situation.

It isn't always obvious what's causing the issue, so the best solution is usually to troubleshoot, checking each potential cause systematically until you've landed on the reason.

Why Do Central Heating Pipes Bang When the Boiler Turns On?

Heating systems, at their core, force hot water or steam through a series of pipes in your home. This hot water warms your radiators and water and should, if all is well, produce very low sound levels.

It's not uncommon to hear a range of suspicious sounds, including:

• Banging and rattling
• Tapping and clicking
• Knocking and clunking
• Vibrating

Some of these noises may be a natural by-product of your boiler and not be something you can easily change.

However, if your pipes start making loud banging noises, it's a sign that there's an issue or breakdown somewhere between your boiler and your taps.

Trapped Air in Central Heating Systems

Trapped air bubbles can cause extremely loud noises but are usually pretty simple to remedy. 

Air in the heating system means bubbles expand and burst, usually indicated by a sudden click or bang.

To resolve this issue, you can:

• Turn off your central heating system, and wait for everything to cool down.
• Bleed your radiators by turning the valves counterclockwise - you'll hear a hiss as the air escapes.
• Close the valve when the hissing stops and water starts to trickle out.
• Turn the system back on, and check whether the noise disturbances have stopped.

Fixing Noisy Expanding Pipes

Another cause is that your heating pipes shift as they become hot and expand slightly. 

This symptom means that your pipes aren't properly secured or supported, and if you follow the noise, you'll usually find that the pipes are hitting a hard surface or wall.

There are lots of ways to correct this, such as:

• Tightening fastenings and mounts that support your pipes.
• Adding small foam pieces to prevent bumps and bangs.

If you have tried to stop pipes from banging and have not been successful, it's worth contacting a professional plumber, as there could be another underlying cause that isn't as apparent.

Water Hammering When Using Taps

Our next issue is water hammering, where you get a loud knocking noise when you turn on your taps - which isn't limited to the hot water.

Water hammering can happen when you use any water source, including the shower or toilet.

That sound means a surge of water is being drawn into the pipes. This action creates excess energy and pressure, although the exact cause depends on the age of your home:

• Properties built before the 1960s often have air chambers, acting as a heating system shock absorber. This air can be displaced by water, so you can turn the water off and drain the water in your pipes through the taps to correct the issue.
• Most modern homes tend to have water hammer arrestors, a spring-loaded shock absorber that rarely fails. 

To fix it, you can fit a water hammer arrestor if you don't already have one, which acts as an overflow device that will soak up excess energy and stop it from impacting your central heating pipework.

Boiler Issues Caused by Limescale Build-ups

Also known as kettling, when limescale accumulates in your heating system, it can block the water flow and impact your boiler and heating.

Most common in hard water areas, you can rectify noises caused by mineral deposits by adding a limescale removal solution to your system.

It tends to be advisable to use a plumber to assist since the level of chemical treatments required will depend on the severity of the blockages. 

Very old radiators and pipes with a large amount of debris may need to be replaced if the build-up is too dense to be removed in this way.

Chemical inhibitors break down heating sludge, and when used alongside a full system flush, they can efficiently remove limescale.

Other options include a magnetic boiler filter to catch tiny metal flakes before they get into the main heating elements.