Which noise is your boiler making?
The type of sound is the best clue to the cause.
| Noise | Most likely cause |
|---|---|
| Gurgling or bubbling | Air in the system, or a partly frozen condensate pipe |
| Kettling, rumbling, boiling sound | Restricted flow through the heat exchanger, often sludge |
| Banging or knocking in pipes | Trapped air, a struggling pump, or loose pipework |
| Bang as the burner lights | Delayed ignition: needs an engineer |
| Whistling or high-pitched whine | Restricted flow, a pump running too fast, or low pressure |
| Humming or vibrating | Pump speed, a loose part, or the fan |
What causes each one?
Gurgling. Air gets into a heating system over time, especially after work on it. It collects at high points and in radiators. In freezing weather, gurgling from the boiler itself is a classic sign the condensate pipe is starting to freeze; see frozen condensate pipe.
Kettling. When water moves too slowly through the heat exchanger it overheats and forms steam bubbles that collapse with a rumbling noise. In hard-water areas limescale is often blamed, but Birmingham is supplied with soft water from the Elan Valley, so here the usual culprit is sludge from corrosion or a pump that is not moving enough water. Left alone, kettling can trip the overheat protection, such as E9 on a Worcester Bosch.
Banging in the pipes. Air pockets, a pump that is failing, or pipes that expand and rub against joists as they heat. Radiators that are cold in places alongside banging point to sludge or air.
Bang on ignition. This is different and more serious. It can mean gas is not lighting straight away. Turn the boiler off and get it checked.
What can you safely check yourself?
- Bleed the radiators with the heating off, then recheck the pressure.
- Check the pressure gauge; low pressure can make pumps noisy.
- In freezing weather, check the condensate pipe outside.
- Make sure radiator valves are open, so water has somewhere to go.
- Note when the noise happens: on start-up, while heating, or with hot water only.
When do you need an engineer?
If noises continue after bleeding, if the boiler kettles or locks out, or if there is any bang on ignition, send an enquiry. Fixes range from adjusting the pump speed to a system clean to remove sludge, often followed by a magnetic filter to keep it clean. The engineer will tell you which, and the price, before any work begins.