UK Boiler Fault Code Database

What's going on with your boiler?

Take a breath. Pick what's happening below — we'll get you a plain-English answer in seconds. No registration, no call-out.

I have a fault code
E.g. E168, F22, A01 — search it and get a plain-English answer.
No hot water but heating works
Radiators hot, taps cold — usually a stuck diverter valve.
Pressure keeps dropping
You top up and it falls again within days — there's a leak somewhere.
Boiler keeps cutting out
Fires up then locks out with a fault code — six common causes.
Banging or kettling noise
Each noise points somewhere — banging, whistling, humming.
Frozen condensate pipe
Common winter cause of lockouts — 10-minute DIY fix.
33,565+ fault codes
29 boiler brands
750+ models covered

Last reviewed Sourced from manufacturer service manuals See our methodology

Browse by manufacturer

Popular boiler brands

All 29 brands →
Vaillant
5,676 codes · 61 models
Worcester Bosch
4,902 codes · 74 models
Baxi
3,754 codes · 63 models
Ideal
2,036 codes · 68 models
Ariston
1,856 codes · 33 models
Alpha
1,817 codes · 44 models
Viessmann
1,463 codes · 16 models
Glow-worm
1,403 codes · 47 models
Ferroli
1,183 codes · 28 models
Potterton
1,060 codes · 44 models
Vokera
949 codes · 34 models
Heatline
823 codes · 16 models
Severity guide

Four levels, four next steps

Every fault on the site is tagged with one of four severities. If you're unsure how worried to be, this is the answer.

Emergency
Turn the boiler off and call a Gas Safe engineer now. Gas escape, carbon monoxide risk, or a fault that could damage the boiler if it keeps running.
High
Book a Gas Safe engineer this week. Boiler may keep running but the fault won't fix itself, and ignoring it usually makes it worse.
Medium
Investigate; book non-urgent service if needed. Usually one part needs attention. Some are DIY-safe; check the page for your code.
Low
Usually a reset or top-up will clear it. Low-pressure codes, routine warnings, conditions you can clear without a tool.

Gas safety first

Gas work must always be carried out by a Gas Safe registered engineer. This site is guidance — never attempt gas repairs yourself. Find a Gas Safe engineer →

How we built this database

Codes sourced from manufacturer service manuals, then enriched with plain-English summaries and DIY guidance. See our methodology →