A boiler fault code is the boiler telling you why it has stopped. Find your brand and code below to see what it means, the safe checks you can try, and whether you need a Gas Safe registered engineer. In Edinburgh, call 0131 210 0505 any time for help.
Smell gas, or a carbon monoxide alarm is sounding? Do not reset the boiler. Open windows, turn off the gas at the meter if it is safe to do so, leave the building and call the free gas emergency line on 0800 111 999. What to do →
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No code on the display? Look up the problem by symptom instead →
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Worcester Bosch EA 227You may be able to fix this
What it means: No flame detected after ignition: the boiler tried to light four times and failed.
What to do: Check other gas appliances work and, on a prepayment meter, that you have credit. In freezing weather, check the condensate pipe is not frozen. Then press reset once.
Worcester Bosch EA 229You may be able to fix this
What it means: The flame went out while the boiler was running. A blocked condensate trap or strong wind into the flue can cause it.
What to do: Check the condensate pipe outside is not frozen or blocked, then reset once. If it returns, call an engineer.
Worcester Bosch EA 338You may be able to fix this
What it means: Too many short burner starts, often because the pump is not detecting enough water.
What to do: Check the pressure gauge. If it is below 1 bar, repressurise to about 1 bar using the filling loop, as shown in your manual.
Worcester Bosch A1 281You may be able to fix this
What it means: The pump is stuck or running in air: little or no water in the system.
What to do: Check the pressure gauge and repressurise to about 1 bar. If the pressure keeps dropping, there may be a leak: call an engineer.
Worcester Bosch LoPrYou may be able to fix this
What it means: Low system pressure (shown on newer Greenstar models such as the 8000 Life).
What to do: Top up the heating water to the pressure shown in your manual using the filling loop.
Worcester Bosch C6 215 / 216Engineer needed
What it means: Fan fault: the fan is running too fast (215) or too slow (216).
What to do: Do not open the boiler. A Gas Safe engineer needs to check the fan and flue.
Worcester Bosch E9 219Engineer needed
What it means: The main heat exchanger has overheated (maximum 105°C).
What to do: Low water pressure or a blocked system can cause overheating. Check the pressure, then call an engineer if it returns.
Worcester Bosch E9 224Engineer needed
What it means: Flue gas thermostat overheat.
What to do: Switch the boiler off and call a Gas Safe engineer.
Worcester Bosch D1 240 / 241Engineer needed
What it means: Return temperature sensor fault: the sensor is wet, disconnected or damaged.
What to do: Needs an engineer. The boiler blocks for a few minutes before locking out.
Worcester Bosch E2 222 / 223Engineer needed
What it means: Flow temperature sensor shorted, disconnected or damaged.
What to do: Needs a Gas Safe engineer to test or replace the sensor.
Worcester Bosch D5Engineer needed
What it means: Condensate pump failure (Greenstar CDi Highflow).
What to do: Needs an engineer.
Worcester Bosch H codes (e.g. H13)You may be able to fix this
What it means: Maintenance codes. They do not stop the boiler. H13 usually means the annual service is due.
What to do: Book a boiler service; there is no need for an emergency callout.
Vaillant F.22You may be able to fix this
What it means: Low water pressure in the system.
What to do: If the gauge reads below 1 bar, Vaillant says a competent person may repressurise using the filling loop. If it keeps dropping, call an engineer.
Vaillant F.28You may be able to fix this
What it means: The flame was not detected during ignition: the boiler failed to light.
What to do: Check other gas appliances, your prepayment meter credit and that the condensate pipe outside is not frozen. If none of these fixes it, call an engineer.
Vaillant F.29You may be able to fix this
What it means: The flame went out during operation and the boiler could not relight.
What to do: Same checks as F.28: gas supply, meter credit and frozen condensate pipe. Then call an engineer.
Vaillant F.54You may be able to fix this
What it means: Fault in the gas supply (shown with F.28 or F.29).
What to do: Check your gas supply and prepayment meter credit. If gas is fine elsewhere, call an engineer.
Vaillant F.75You may be able to fix this
What it means: No pressure change was detected when the pump started (Vaillant groups it with the same pressure advice as F.22).
What to do: Vaillant gives the same advice as F.22: check and top up the pressure if below 1 bar, otherwise call an engineer.
Vaillant F.20You may be able to fix this
What it means: The safety thermal cut-out has operated and shut the boiler off (overheat).
What to do: Check the pressure, look for leaks, make sure radiator valves are open and bleed any trapped air. If it returns, call your installer.
Vaillant F.27Engineer needed
What it means: A flame signal was detected while the burner is off.
What to do: Vaillant says this is for an expert only. Do not attempt it yourself.
Vaillant F.32Engineer needed
What it means: Fan fault.
What to do: Needs a Gas Safe engineer.
Vaillant F.35Engineer needed
What it means: The air or flue pipe is blocked.
What to do: Switch the boiler off and call an engineer or your installer.
Vaillant F.0 / F.1Engineer needed
What it means: The flow (F.0) or return (F.1) temperature sensor has been interrupted.
What to do: Needs an engineer.
Vaillant F.83You may be able to fix this
What it means: When the burner starts, little or no temperature rise is registered at the flow or return sensor.
What to do: Vaillant advises contacting your installer. Checking the pressure gauge first is still worthwhile.
Vaillant F.88Engineer needed
What it means: The electrical connection to the gas valve has been interrupted.
What to do: Needs a Gas Safe engineer.
Ideal F1You may be able to fix this
What it means: Low pressure.
What to do: Top up the system pressure to between 1 and 1.5 bar using the filling loop, as shown in your manual.
Ideal L2 / F2You may be able to fix this
What it means: Flame loss or ignition lockout: the boiler could not light or keep its flame.
What to do: Reset the boiler. Check your gas supply, prepayment credit and that the yellow gas isolation valve is open. If the boiler gurgles while trying to fire, the condensate pipe may be blocked or frozen.
Ideal L1You may be able to fix this
What it means: Flow temperature overheat or no water flow.
What to do: Make sure all radiator valves are open and the pressure is between 1 and 1.5 bar, then reset.
Ideal L3You may be able to fix this
What it means: No water flow.
What to do: Check the pressure (1 to 1.5 bar), bleed the radiators, recheck the pressure, then reset.
Ideal L5You may be able to fix this
What it means: The boiler has been reset too many times in 15 minutes.
What to do: Turn the power off and on again. If the original fault returns, call an engineer.
Ideal L6Engineer needed
What it means: False flame lockout.
What to do: Reset once. If it persists, a Gas Safe engineer is needed.
Ideal F3Engineer needed
What it means: Fan fault.
What to do: Reset once. If it persists, a Gas Safe engineer is needed.
Ideal F4 / F5Engineer needed
What it means: Flow (F4) or return (F5) thermistor fault.
What to do: Reset once. If it persists, an engineer is needed.
Ideal F6Engineer needed
What it means: Outside sensor fault.
What to do: Reset once. If it persists, an engineer is needed.
Ideal F7Engineer needed
What it means: Low mains voltage.
What to do: Ideal advises a local electrician checks the property's electrics.
Ideal F0Engineer needed
What it means: No water flow thermistor.
What to do: Reset once. If it persists, an engineer is needed.
Ideal C0 / C2Engineer needed
What it means: Boiler control chip (BCC) activation or chip fault.
What to do: Reset once. If it persists, an engineer is needed.
Baxi E133You may be able to fix this
What it means: Gas supply interrupted or the flame failed to ignite. Baxi also lists it among the codes shown when the condensate pipe is frozen.
What to do: Check other gas appliances and prepayment credit. In freezing weather, thaw the condensate pipe with warm (not boiling) water, then restart.
Baxi E119You may be able to fix this
What it means: Low water pressure. Baxi also lists it among codes that can appear with a frozen condensate pipe.
What to do: Check the gauge and repressurise to the level in your manual. In a cold snap, check the condensate pipe too.
Baxi E118You may be able to fix this
What it means: Water pressure too low.
What to do: Repressurise using the filling loop as shown in your manual. If it keeps dropping, there may be a leak.
Baxi E28You may be able to fix this
What it means: Flue or sensor fault, most often caused by a frozen or blocked condensate pipe.
What to do: Baxi's advice: switch off, warm the exposed condensate pipe along its length, then restart. Repeat if needed.
Baxi E125You may be able to fix this
What it means: Circulation fault in the primary (heating) circuit, often linked to low pressure.
What to do: Check the pressure and bleed radiators if they are cold at the top. If it returns, call an engineer.
Baxi E117Engineer needed
What it means: Water pressure too high.
What to do: Do not keep resetting. A Gas Safe engineer should check the filling loop, expansion vessel and pressure relief valve.
Baxi E110Engineer needed
What it means: Safety thermostat operated: the boiler has overheated.
What to do: Check the pressure and that radiator valves are open. If it returns, call an engineer.
Baxi E130Engineer needed
What it means: Flue sensor operated (flue overheat).
What to do: Switch off and call a Gas Safe engineer.
Baxi E160Engineer needed
What it means: Fan fault.
What to do: Needs a Gas Safe engineer.
Baxi E20Engineer needed
What it means: Central heating temperature sensor (NTC) fault.
What to do: Needs an engineer.
Viessmann F2Engineer needed
What it means: The boiler temperature limiter has tripped (overheat).
What to do: Check the pressure gauge. Do not keep resetting; call a heating engineer.
Viessmann A4Engineer needed
What it means: Maximum system pressure exceeded.
What to do: Do not top up. Call a heating engineer.
Viessmann F1Engineer needed
What it means: Flue gas temperature has exceeded its limit.
What to do: Switch off and call a Gas Safe engineer.
Viessmann F8Engineer needed
What it means: The fuel (gas) valve closes late.
What to do: Switch off and call a Gas Safe engineer.
Viessmann E5Engineer needed
What it means: Flame amplifier fault; the burner is blocked.
What to do: Needs a Gas Safe engineer.
Viessmann 30 / 38Engineer needed
What it means: Boiler temperature sensor short circuit (30) or open circuit (38); the burner is blocked.
What to do: Needs an engineer.
Viessmann 50Engineer needed
What it means: Cylinder temperature sensor short circuit: no hot water.
What to do: Heating may still work. Call an engineer.
Viessmann 10 / 18You may be able to fix this
What it means: Outdoor temperature sensor fault; the control runs as if it is 0°C outside.
What to do: The heating keeps working, so this can usually wait for a planned visit.
Viessmann A7Engineer needed
What it means: Control panel defective.
What to do: Needs an engineer.
Viessmann b5 / F0 / FFEngineer needed
What it means: Internal control fault (FF can also mean the reset button is stuck).
What to do: Needs an engineer.