Here’s What It Means
If your boiler is making noise when heating on, it’s usually a sign that something in the system isn’t working as smoothly as it should. Many homeowners notice that their boiler seems quiet when it’s idle or only heating water, but as soon as the heating switches on, unusual sounds begin. These can include banging, humming, whistling, gurgling, or vibrating noises, and while some are harmless, others indicate an issue that should be checked sooner rather than later.
Boiler noise is most noticeable when the heating is on because this is when the system is under the greatest demand. More water is being heated and circulated, pressure changes occur, and internal components like pumps and valves are working harder. If there’s a fault, buildup, or imbalance, the noise often appears at this stage.
Why Is My Boiler Making Noise When the Heating Is On?
One of the most common reasons a boiler makes noise when heating is on is kettling. This occurs when limescale or sludge builds up inside the heat exchanger, restricting water flow. As the water overheats, it starts to boil and form steam bubbles, creating loud banging or rumbling noises similar to a kettle. Kettling is particularly common in hard water areas and in systems that haven’t been serviced or flushed regularly. If ignored, it can reduce efficiency and cause long-term damage to the boiler.
Another frequent cause is trapped air within the heating system. When air pockets form, water can’t circulate smoothly, leading to gurgling or bubbling noises once the heating is running. This can also result in radiators heating unevenly or feeling cold at the top. Low or unstable boiler pressure can also cause noise. When pressure drops below the recommended level, the boiler struggles to circulate water properly, which can lead to humming, vibrating, or rattling sounds during heating cycles.
In some cases, the noise may come from a worn or failing pump. The pump moves hot water around your heating system, and when it becomes worn, blocked, or strained, it can produce loud whirring or grinding noises when the heating turns on. Pipework can also be responsible. As pipes heat up, they expand, and if they’re tight against walls or floorboards, this expansion can cause clicking or tapping sounds. While this is usually harmless, it’s still worth checking to rule out more serious issues.
Is a Noisy Boiler Something to Worry About?
A boiler making noise when heating is on isn’t always dangerous, but it should never be ignored. Noises are often early warning signs that something isn’t functioning correctly. Left untreated, minor issues can lead to reduced heating performance, higher energy bills, unexpected breakdowns, or costly repairs. If the noise is getting louder, happening more often, or affecting how well your heating works, it’s a clear sign that professional attention is needed.
What You Can Check Before Calling an Engineer
Before booking a repair, there are a few simple checks you can safely make:
Look at your boiler pressure to see if it’s within the normal range
Notice whether the noise only happens when the heating is on
Check if radiators are heating evenly throughout the house
If the problem persists after these checks, it’s important not to attempt any internal fixes yourself. Boilers are gas appliances, and repeated resetting or ignoring the issue can make things worse.
Call a Boiler Engineer Before the Problem Gets Worse
If your boiler is making noise when heating on, don’t wait for it to fail completely. At Plumbing Immediately, our Gas Safe registered engineers can quickly identify the cause of the noise, whether it’s kettling, trapped air, pressure issues, or a failing pump and carry out professional repairs to restore your heating system to quiet, efficient operation. Call us today to book a boiler engineer and ensure your home stays warm and safe, without any worrying noises.
Is your boiler making noise when heating on?
Don’t wait until it breaks down! Call Plumbing Immediately today and get a Gas Safe engineer to fix it fast. Quiet, safe and efficient heating is just a phone call away.