What's your boiler doing?
Search any fault code — or tell us what's wrong below. We'll walk you through it, then get you a Gas Safe engineer if you need one.
No code on the display? Tell us what it's doing
Pick the closest symptom for safe steps you can try — and a Gas Safe engineer if it needs one.
Heating might still work, but hot water won't — here's the usual order to check.
- 1Check the boiler display for a fault code and note it down.
- 2Make sure the hot-water / cylinder setting is switched on, not just heating.
- 3Check other taps — is it every tap, or just one?
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A pressure gauge below 1 bar will stop the boiler. Sometimes a top-up fixes it; a repeat drop means a leak.
- 1Read the pressure gauge — normal is roughly 1 to 1.5 bar when cold.
- 2If low, use the filling loop to top up slowly to ~1.2 bar.
- 3Watch it over a few days. If it keeps dropping, there is a leak.
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Rumbling or banging (“kettling”) is usually limescale or trapped air restricting flow.
- 1Note when it happens — on startup, or when hot water runs?
- 2Bleed radiators to release trapped air.
- 3If noise continues, the heat exchanger may need a professional flush.
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Cold at the top usually means trapped air; cold at the bottom means sludge.
- 1Turn the heating on and feel across each radiator.
- 2Bleed the ones that are cold at the top with a radiator key.
- 3Re-check system pressure afterwards and top up if needed.
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Frequent cut-outs point to pressure, thermostat or circulation problems.
- 1Check the pressure gauge first — low pressure is the most common cause.
- 2Note any fault code shown when it cuts out.
- 3Check the room thermostat batteries and settings.
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Nothing happening at all — work through power, gas and pressure.
- 1Confirm the boiler has power and the display is lit.
- 2Check other gas appliances work (so gas supply is on).
- 3Check pressure and any fault code on the display.
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Popular guides
Boiler fault code lookup for every UK brand
BOYLA helps homeowners and Gas Safe engineers decode boiler faults fast. Enter the code on the display, or tell us the symptom, to see what it means, the most likely causes, safe step-by-step checks, and when to call a professional — across Worcester Bosch, Vaillant, Baxi, Ideal, Glow-worm and more.
BOYLA is an independent resource. Some links are affiliate links — we may earn a commission at no cost to you. Always use a Gas Safe registered engineer for gas work.