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Bosch / Junkers error codes
The most common codes for Bosch gas boilers (Condens) and Junkers boilers (Cerapur, Cerasmart), with what they mean and what to do.
Junkers became Bosch. Older Junkers boilers show two characters (EA, CE…), recent Bosch boilers a number (227, 1017…): both are in the list.
No flame detected at start-up.
IgnitionCheck that the gas tap is open, then reset the boiler once. If the code comes back, don't keep trying: repeated resets can lock the appliance. Call us.
The system pressure is too low.
PressureCheck the pressure gauge. If it's too low, top up the water (if you know how) and bleed the radiators. If the pressure drops again, there's probably a leak: call us.
The overheat safety cut the boiler out: often low water, air in the system or a pump problem.
CirculationCheck the pressure and that the radiator valves are open. If everything looks fine and the code comes back, the water circulation needs checking (pump, bleeding, sensors): call us.
The pump ran dry: air in the system, pressure too low or a seized pump.
CirculationCheck the pressure and that the radiator valves are open. If everything looks fine and the code comes back, the water circulation needs checking (pump, bleeding, sensors): call us.
The fan is running too slowly: the fan or the flue needs checking.
Flue · safetySwitch the boiler off and air the room. This code concerns the flue: call us. If a CO alarm goes off, or anyone has a headache or nausea, get everyone outside and call 112.
A flame is still detected after the boiler has shut down.
TechnicianA component or electronics fault: this needs a technician. Don't open the boiler; call us and give the code shown.
The flow temperature sensor is faulty or disconnected.
TechnicianA component or electronics fault: this needs a technician. Don't open the boiler; call us and give the code shown.
The hot water temperature sensor is faulty or its cable is broken.
TechnicianA component or electronics fault: this needs a technician. Don't open the boiler; call us and give the code shown.
No flame detected at ignition. After 5 attempts, the boiler locks out.
IgnitionCheck that the gas tap is open, then reset the boiler once. If the code comes back, don't keep trying: repeated resets can lock the appliance. Call us.
The flame went out during operation.
IgnitionCheck that the gas tap is open, then reset the boiler once. If the code comes back, don't keep trying: repeated resets can lock the appliance. Call us.
The system pressure is too low.
PressureCheck the pressure gauge. If it's too low, top up the water (if you know how) and bleed the radiators. If the pressure drops again, there's probably a leak: call us.
The water pressure is too low (the boiler flags it without stopping).
PressureCheck the pressure gauge. If it's too low, top up the water (if you know how) and bleed the radiators. If the pressure drops again, there's probably a leak: call us.
The temperature limiter (heat exchanger or flue gas) has tripped.
CirculationCheck the pressure and that the radiator valves are open. If everything looks fine and the code comes back, the water circulation needs checking (pump, bleeding, sensors): call us.
The pump is seized or running dry.
CirculationCheck the pressure and that the radiator valves are open. If everything looks fine and the code comes back, the water circulation needs checking (pump, bleeding, sensors): call us.
The boiler temperature is rising too fast: the water isn't circulating well.
CirculationCheck the pressure and that the radiator valves are open. If everything looks fine and the code comes back, the water circulation needs checking (pump, bleeding, sensors): call us.
Flue problem: the flue is blocked, missing or badly connected.
Flue · safetySwitch the boiler off and air the room. This code concerns the flue: call us. If a CO alarm goes off, or anyone has a headache or nausea, get everyone outside and call 112.
The air pressure switch has opened: the condensate trap needs cleaning.
Flue · safetySwitch the boiler off and air the room. This code concerns the flue: call us. If a CO alarm goes off, or anyone has a headache or nausea, get everyone outside and call 112.
A flame signal is detected while the burner is off.
TechnicianA component or electronics fault: this needs a technician. Don't open the boiler; call us and give the code shown.
This code isn't in the list: call us and give it to us, we'll tell you straight away what's going on.
Source: Bosch, Condens 2300i W installation and maintenance manual (6721825838); Junkers Belgium, Heatronic III diagnostic codes (10.2011). Codes and how they're shown can differ between models: if in doubt, your appliance's manual applies.
First steps
- Write down the code shown: it saves us time.
- Check the pressure gauge.
- Check that the gas tap is open.
- Reset once. If the code comes back, call us.
Practical guides: Top up the pressure · Bleed a radiator · Reset the boiler
A breakdown, a question? Get in touch.
Call us or message us on WhatsApp. Or leave your number, with a photo of the boiler if you like: we'll call you back.
