Every manufacturer uses its own code system, but the faults behind the codes repeat across all of them: low water pressure, a flame that won't light or won't stay lit, a frozen condensate pipe, and sensor or fan trouble. Two checks are worth making on any boiler before you go further: if the pressure gauge reads below 1 bar, topping the system up via the filling loop can clear a low-pressure code; and in freezing weather, the white plastic condensate pipe running outside can freeze and lock the boiler out — thaw it with warm (never boiling) water, then reset once. Anything involving ignition, the gas valve or the flue needs a Gas Safe registered engineer.
Worcester Bosch error codes
Greenstar boilers show a fault code paired with a cause code — "EA 227", for example — and it's the pair together that identifies the fault. The newer 4000 and 8000 ranges use standalone numeric codes.
| Code | What it means | Typical cause |
|---|---|---|
| EA 227 | The boiler tried to ignite but no flame was detected | Frozen condensate pipe, or an interruption to the gas supply |
| EA 229 | The flame lit, then was lost while the boiler was running | Gas supply or combustion problem that needs proper investigation |
| E9 224 | Overheat — the flue or high-limit thermostat has tripped | Flue or fan problem; needs inspecting, not repeated resetting |
| A1 281 | The pump is stuck or running dry | Seized pump, or too little water in the system — check the pressure gauge first |
| 1017 | System water pressure too low (4000/8000 ranges) | Gradual pressure loss — if it keeps dropping after a top-up, there's a leak |
| FA 306 | A flame signal is still detected after the gas valve has closed | Possible gas valve fault — stop using the boiler and call an engineer straight away |
Book a Diagnosis — £99 Worcester Bosch repairs →
Vaillant error codes
Vaillant's ecoTEC, ecoFIT and turboTEC ranges use F-prefixed codes — "F." followed by two digits.
| Code | What it means | Typical cause |
|---|---|---|
| F.22 | System water pressure too low | Normal gradual pressure loss, or a leak if it keeps recurring — top up via the filling loop |
| F.28 | Ignition failure — the boiler tried to light and couldn't | Gas supply interruption or a frozen condensate pipe; one reset at most |
| F.29 | The flame lit successfully, then was lost during operation | Gas supply or condensate trouble — needs an engineer if it returns |
| F.54 | No gas inlet pressure, or not enough to start | Supply problem — check another gas appliance in the house works, then call an engineer |
| F.62 | The gas valve shut off later than it should after the flame went out | Gas valve fault — a safety concern, so stop using the boiler |
| F.75 | No water movement detected when the pump runs | Stuck pump or a faulty pressure sensor |
Book a Diagnosis — £99 Vaillant repairs →
Baxi error codes
Baxi's Duo-tec, Platinum and 600/800 ranges use three-digit E-codes. The exact set varies a little between ranges, so check the label inside the casing flap for your model.
| Code | What it means | Typical cause |
|---|---|---|
| E110 | Overheat lockout — the flow temperature passed its safe limit | Low pressure, closed radiator valves or poor circulation; one reset at most |
| E118 / E119 | System water pressure too low | Pressure has dropped below about 0.5 bar — top up to 1–1.5 bar; repeated drops mean a leak |
| E125 | Circulation fault — water isn't moving round the system properly | Pump problem, airlock or a sludge blockage |
| E133 | Ignition failed, or the gas supply was interrupted | Gas supply off, or a frozen condensate pipe in cold weather |
| E160 | Fan fault | Fan not running or not reaching speed — part of the flue system, so engineer only |
| E168 | General fault | Often follows a power interruption — worth one reset, then an engineer if it returns |
Book a Diagnosis — £99 Baxi repairs →
Ideal error codes
Ideal's Logic, Logic+ and Vogue ranges mix F- and L-prefixed codes depending on the model and control board fitted.
| Code | What it means | Typical cause |
|---|---|---|
| F1 | Low system water pressure | Gradual pressure loss — top up via the filling loop |
| L2 / F2 | Ignition lockout — the flame never established, or was lost | Gas supply interruption or a frozen condensate pipe; one reset only |
| F3 | Fan fault | The fan or its wiring — engineer diagnosis needed |
| F4 / L4 | Flow thermistor fault | The sensor measuring water leaving the boiler is out of range |
| F9 / L9 | Control board (PCB) fault | The boiler's electronics — nothing safe to check yourself |
| LC | Five resets within 15 minutes — the boiler stops accepting more | An underlying fault (often F1 or L2) that needs diagnosing, not more resets |
Book a Diagnosis — £99 Ideal repairs →
Potterton error codes
Potterton is part of the Baxi Heating family — its Promax, Titanium and Gold ranges use E-prefixed codes.
| Code | What it means | Typical cause |
|---|---|---|
| E119 | Central heating pressure has fallen below 0.5 bar | Pressure loss — top up to 1–1.5 bar with the boiler cold; recurring drops mean a leak |
| E133 | Ignition failure, or an interruption to the gas supply | Gas supply off, or a frozen external condensate pipe in winter |
| E110 | The overheat (safety) thermostat has operated | Primary water overheated — one careful reset, then an engineer if it returns |
| E125 | Circulation fault — the boiler lit but water isn't moving properly | Pump problem, airlock or low pressure |
| E28 | Flue sensor fault, or a blocked flue or condensate drain | Frozen condensate pipe in winter; otherwise a possible flue blockage — treat with caution |
| E160 | Fan fault | The fan or its wiring — engineer only |
Book a Diagnosis — £99 Potterton repairs →
This is general guidance, not a diagnosis — the same code can point to more than one underlying cause depending on the model and history of the boiler. If a code keeps recurring after a reset, that's a sign it needs a proper look rather than repeated resetting.