A rumble, a bang or a noise like a kettle coming to the boil, every time the heating fires up. It is called kettling, and it is worth acting on.
What is going on
Inside the boiler, water passes through the heat exchanger and gets heated. If the inside of the heat exchanger is coated, with limescale or with the black sludge that builds up in a heating system, the water cannot flow and pick up heat evenly. It boils in patches. The bubbles collapsing are the noise you hear.
Why not ignore it
Left alone, kettling shortens the life of the boiler. The heat exchanger is working harder and hotter than it should, and it is one of the most expensive parts to replace. A noisy boiler is often a boiler being slowly damaged.
What usually causes it
- Sludge from corrosion in the radiators, collecting in the heat exchanger. Often you will see black water when you bleed a radiator, and radiators cold along the bottom.
- Limescale, more of a problem in harder water areas.
- Low flow, for example a pump not running properly or a valve partly closed.
What we check
The symptom first: when it happens, whether it is the heating or the hot water, and whether the radiators show signs of sludge. Then the boiler itself. If it is sludge, the answer is usually a powerflush with a magnetic filter fitted afterwards. If it is a part, the repair is priced once the fault is known.
Repair or replace?
If the heat exchanger is badly damaged and the boiler is old, you get both numbers in front of you: the repair and a fixed price for a new boiler. New boilers are fitted from £1,900 with VAT, with the flush and filter included. You decide. Tell us what it sounds like.