Free Guide
5 Most Common Boiler Issues — and What They Actually Mean
Before you book an engineer, it helps to know what you're likely dealing with. Here's what causes the 5 issues we see most often, and whether it's usually a quick fix or a sign your boiler's on its way out.
1. No Heating or Hot Water
Usually points to an ignition fault, a failed printed circuit board (PCB), or a faulty thermostat/programmer not telling the boiler to fire. On combi boilers it can also be a diverter valve stuck in the wrong position.
Quick fix or replacement? Often a straightforward repair — a PCB or diverter valve replacement is common and cost-effective on a boiler under 8–10 years old. On an older boiler, it's worth weighing the repair cost against a new installation, especially if this isn't the first fault.
2. Losing Pressure
A boiler that keeps dropping below 1 bar usually has a small leak somewhere in the system — a pressure relief valve, a radiator valve, or a joint in the pipework — or, less commonly, a failing expansion vessel.
Quick fix or replacement? Usually a quick fix — re-pressurising is simple, but if it keeps happening the actual leak needs finding and fixing rather than just topping up pressure every few weeks.
3. Kettling or Banging Noises
A kettle-like rumbling or banging from the boiler is almost always limescale or sludge building up around the heat exchanger, restricting water flow and causing it to overheat locally. This is especially common in hard-water areas across Yorkshire.
Quick fix or replacement? A power flush usually clears it and protects the system going forward. Left untreated, it accelerates wear on the heat exchanger, which is one of the more expensive parts to replace.
4. Pilot Light Keeps Going Out
Mainly an issue on older, non-condensing boilers. Usually a worn thermocouple (the safety sensor that detects the pilot flame) or a draught affecting the flame. Occasionally a faulty gas valve.
Quick fix or replacement? A thermocouple replacement is inexpensive. That said, if your boiler still has a pilot light, it's likely 15+ years old and significantly less efficient than a modern condensing boiler — worth at least getting a replacement quote to compare running costs.
5. Radiators Not Heating Evenly
Cold patches at the top of a radiator usually mean trapped air — a quick bleed sorts it. Cold at the bottom instead usually means sludge build-up, which needs a power flush rather than bleeding.
Quick fix or replacement? Bleeding radiators is a 5-minute job. Sludge is more involved but still a repair, not a replacement issue — though it's worth having the whole system checked if several radiators are affected at once.
None of this replaces an actual diagnosis — if in doubt, book a service or repair and we'll tell you straight whether it's worth fixing or replacing, based on your system's age and condition, not on what's easiest to sell.