Your boiler is showing a code. Three or four characters, sometimes red, sometimes flashing — and zero heating. Welcome to the most-Googled topic in UK plumbing.
The good news: those codes are not random. They are the boiler's built-in fault diagnosis system, and once you know what each one means, you can often save yourself a callout. We see all four of these brands every week across Burnley, Blackburn, Preston and the wider Lancashire area, so this is the working-engineer's decode for 2025.
Before you start — the safety bit
Two ground rules. One: you can legally reset a boiler, top up its pressure, and inspect its external pipework. Two: you can never open the boiler casing, touch internal gas components, or replace parts unless you are Gas Safe registered. Doing so is a criminal offence in the UK and invalidates your home insurance.
If you smell gas at any point — even faintly — call the National Gas Emergency line on 0800 111 999 first, then us.
Worcester Bosch fault codes (Greenstar 4000, 8000, CDi, Si, i)
Worcester Bosch is the UK's most-fitted boiler brand, so we see these codes the most.
- F22 — Low system pressure. Easily the most common Worcester fault. Top up via the filling loop (under the boiler) to 1.0–1.5 bar when cold. If the pressure drops again within a week, you have a leak or a failing expansion vessel. Typical repair: £85 callout, £180–£280 for a new expansion vessel.
- F75 — Pump sensor fault. The pump is not detecting flow. Usually caused by an airlock, a sticking pump, or a sensor coated in sludge. A powerflush resolves this in around 70% of cases we see. Typical repair: £85 diagnostic, then £450+ for a powerflush or £220 for a pump.
- F1 — Frozen condensate or low pressure. In winter this is nearly always a frozen condensate pipe. In summer it usually means pressure has dropped below 0.5 bar.
- EA — Loss of flame. Worcester's way of saying the gas is not igniting. Could be a faulty ignition lead, dirty electrodes, or gas-supply issue. Always needs a Gas Safe engineer. Typical repair: £180–£320.
- D1/D7 — NTC sensor faults. A thermistor (temperature sensor) has failed. Cheap part, quick fix. Typical repair: £140–£180 all-in.
Worcester reset method: hold the reset button (the spanner/flame icon) for 5 seconds. If the same code comes back within minutes, it is a hard fault — book a repair.
Baxi fault codes (200, 600, 800, Platinum, Duo-tec)
Baxi codes start with E (error) or L (lockout). The 800 and Platinum ranges are the most common in 2020+ Lancashire installs.
- E125 / E160 — Insufficient circulation / fan fault. Pump or fan related. Air in the system, a sticking pump, or a tired fan motor. Typical repair: £180–£280.
- E133 — Ignition lockout / no gas. Three failed ignition attempts. Check that your gas meter has not tripped, the gas supply is on, and no other gas appliances have gone off. Repair needs a Gas Safe engineer. Typical: £140–£260.
- E168 — General boiler fault. Frustratingly vague. PCB diagnostic required. Typical repair: £85 callout, plus parts depending on what the PCB reads.
- E118 — Low water pressure. Same fix as Worcester F22 — top up to 1.0–1.5 bar.
- E110 — Overheat lockout. Limit thermostat has tripped because of a flow restriction — often sludge or a stuck pump. Almost always indicates a system clean is needed. Typical repair: £450+ powerflush.
Baxi reset method: press and hold the reset button (often labelled with an “R”) for 5 seconds.
Vaillant fault codes (ecoTEC Plus, Pro, Exclusive)
Vaillant uses F-codes similar to Worcester, but with slightly different meanings. Their fault display is one of the clearer ones once you know the system.
- F22 — Low water pressure (Vaillant). Vaillant's version is the same fix as Worcester F22 — top up the system pressure. The filling loop on most ecoTEC models is on the underside or right-hand side.
- F23 — Large temperature differential. Heating water is leaving hot but coming back too cold. Almost always pump failure or a partially blocked heat exchanger. Typical repair: £180–£320.
- F28 / F29 — Ignition failure. Gas supply, gas valve, or ignition components. Gas Safe engineer required. Typical: £180–£300.
- F75 — Pump pressure sensor fault. Same family of fault as Worcester F75 — usually sludge-related. Powerflush often the answer.
- F62 / F63 — Gas valve shutdown. Serious — gas valve has shut down. Do not reset more than once. Call a Gas Safe engineer immediately.
Ideal fault codes (Logic+, Vogue, Mexico)
Ideal's codes are mostly L-codes (lockouts), though some newer Vogue models use F-codes.
- L2 — Ignition lockout. Three failed ignition attempts. Same diagnostic as Baxi E133 — check gas supply, then call an engineer.
- L5 — Repeated reset lockout. The boiler has been reset 5+ times in a short period and has locked itself out for safety. You must wait 10–15 minutes before another reset.
- F1 — Low water pressure. Top up to 1.0–1.5 bar cold.
- F2 — Flame loss. Gas supply, dirty electrodes, or PCB. Engineer needed.
- F9 — Internal fault / PCB. Cannot be reset — needs a Gas Safe engineer to diagnose with manufacturer tooling.
The three safe DIY fixes (any brand)
- Top up pressure. Find the filling loop (silver braided hose under the boiler). Open both valves until the pressure gauge reads 1.0–1.5 bar cold. Close both valves. Hit reset.
- Reset the boiler. Hold the reset button for 5 seconds. If the code returns within minutes, stop — it is a hard fault.
- Check the condensate pipe. White plastic pipe running outside the property. If you can see ice or it sounds gurgly, follow our condensate-thawing guide.
Anything beyond these three steps — case off, gas controls, internal sensors — is a Gas Safe engineer job by law.
What does a boiler repair typically cost in Lancashire (2025)?
- £85 — fixed-price diagnostic callout (Mon–Sat daytime)
- £120 — emergency / out-of-hours diagnostic
- £140–£220 — common repairs (thermistors, fans, ignition leads)
- £180–£320 — expansion vessels, pumps, diverter valves
- £280–£550 — PCB replacement, plate heat exchanger
- £450–£950 — full powerflush (often needed before warranty work)
When a fault code means you need a new boiler
Most fault codes are repairs, not write-offs. But if you see repeated PCB faults on a 10+ year old boiler, or your heat exchanger has scaled or sludged enough to keep tripping the system, replacement often makes more economic sense than another £550 part on a boiler nearing end of life. See our 2025 Lancashire boiler replacement cost guide for honest figures.
Get a fault diagnosed today
If your code does not clear after a reset and a pressure top-up, get a Gas Safe engineer out. We cover Burnley, Preston, Blackburn, Nelson, Colne, Accrington, Clitheroe and the wider Lancashire area same-day. Call 01282 914 044 or request a callback — tell us the fault code and we will usually carry the part on the van.