Blocking fault
The boiler stops while a condition is out of range (temperature, pressure, voltage) and starts again on its own once it is back to normal. If the same blocking fault lasts, it turns into a locking fault.
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Bosch Error Codes
Your Bosch boiler (Condens 2300, 5300, 7000, former Junkers Cerapur…) shows two characters such as EA, E9 or A1? The table below gives the meaning of each one. Bosch distinguishes blocking faults, which clear themselves once the cause disappears, from locking faults, which keep the boiler stopped until someone intervenes.
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Repairing a Bosch boiler that has stopped
On a Bosch condensing boiler, the display shows a short code (EA, E9, C6…) and, in the service menu, a three-digit number (227, 224, 215…). That second number is what matters to the engineer: one letter code can hide four or five different situations.
The most frequent call-outs concern EA (no flame), E9 (overheating protection), A1 (no pressure from the pump) and the fan family C6 / C7. Each one points to a different set of parts, and the technician tests them one by one with a multimeter and a flue gas analyser.
Once the cause is known, you get the price of the repair before he starts. Electrodes, sensors and fans for the common Bosch ranges are in his van, so most boilers are running again the same visit.
Servicing a Bosch condensing boiler
A condensing boiler produces acidic water that runs through a siphon. When the siphon clogs, or when the heat block gets dirty, codes such as EA 227 or E9 224 start to appear in winter.
The yearly service removes those causes: cleaning of the heat block and condensate trap, inspection of the electrodes, adjustment of the air/gas ratio, test of the safety devices, then the service attestation. The H13 reminder on the screen simply means that this visit is due.
Bosch error code table
Search for your code: the first column is the code on the display, the second the service number shown in the menu. Both together give the exact fault.
| Code | Service code | Meaning | What the technician checks |
|---|---|---|---|
| 0Y | 276 | Flow temperature above 95 °C (blocking fault) | Operating pressure, shut-off valves, boiler pump, pump cable and pump setting. |
| 9A | 235 / 360 / 361 / 362 | Incorrect coding card (locking fault) | Coding card. |
| 9U | 233 | Coding card not recognised (locking fault) | Seating of the coding card, replaced if necessary. |
| A1 | 281 | The heating pump builds up no pressure (blocking fault) | Operating pressure, shut-off valves, air in the appliance, boiler pump. |
| A8 | 323 | BUS communication interrupted (blocking fault) | BUS cable between the controller and the boiler. |
| C1 | 264 | Fan defective (blocking fault) | Fan wiring harness and plug, dirt or blockage in the fan. |
| C4 | 273 | Burner and fan have run non-stop for a full day: short safety shutdown | Information: the boiler starts again by itself after the test. |
| C6 | 215 | Fan running too fast (locking fault) | Flue gas system, cleaned or repaired if needed. |
| C6 | 216 | Fan running too slowly (locking fault) | Fan wiring harness, dirt or blockage in the fan. |
| C7 | 214 | Fan switched off during the safety time (locking fault) | Fan wiring and fan. |
| C7 | 217 | Fan not working (locking fault) | Fan wiring and fan. |
| D3 | 232 | Jumper missing on the terminals for external thermostat TB 1 | Connection terminals of the external switch. |
| D4 | 341 | Temperature rising too fast in heating mode | Operating pressure, valves, boiler pump and its setting. |
| D5 | 330 | External flow sensor (low loss header) short-circuited | Sensor and connecting cable. |
| D5 | 331 | External flow sensor (low loss header) interrupted | Sensor and connecting cable. |
| E2 | 350 | Flow temperature sensor short-circuited | Sensor and connecting cable. |
| E2 | 351 | Flow temperature sensor interrupted | Sensor and connecting cable. |
| E9 | 224 | Thermostat, flue gas temperature limiter or differential pressure switch has tripped | Heat block and limiters, flue gas system, pressure switch hose, pump, water circuit of the heat block. |
| EA | 227 | Flame not detected; becomes a locking fault from the 4th ignition attempt | Gas valve and supply pressure, electrodes and cables, flue, air/gas ratio, condensate trap, gas valve block. |
| EA | 229 | No ionisation signal while the burner is running | Ionisation electrode and its cable. |
| EA | 261 | Timing error during the first safety time (locking fault) | Connectors and wiring to the control unit, control unit. |
| EH | 258 | System fault in the control unit or coding card (locking fault) | Connections to the control unit, control unit. |
| F0 | 238 | Gas valve cable, gas valve or control unit defective (locking fault) | Wiring, gas valve block, control unit. |
| F0 | 239 | Internal fault (locking fault) | Coding card, control unit. |
| F0 | 280 | Timing error during a restart attempt (locking fault) | Connectors, wiring, control unit. |
| F0 | 290 | Internal fault (blocking fault) | Connectors, ignition cables, air/gas ratio, control unit. |
| F7 | 228 | Flame detected while the burner is off (locking fault) | Electrodes, flue gas system, moisture on the circuit board. |
| F0 / F7 / Fd | 356 / 328 / 231 | Mains voltage interrupted or too low | Power supply to the boiler (socket, circuit breaker). |
| FA | 306 | Flame detected after the gas has been shut off (locking fault) | Gas valve block, condensate trap, electrodes, flue. |
| FA / Fb | 364 / 365 | Flame detected after the gas has been shut off (locking fault) | Gas valve block, electrodes and cable, condensate trap, flue. |
| H11 | - | Domestic hot water temperature sensor defective (reminder) | Sensor and connecting cable. |
| H12 | - | Cylinder temperature sensor defective (reminder) | Sensor and connecting cable. |
| H13 | - | Inspection date reached (reminder) | Annual boiler service. |
Code not in this table: call us, our technician knows it.
Smell of gas? Do not touch any switch, open the windows, leave the house and call 112 from outside. For any other code, write it down and call us: the technician knows what to look at and brings the right parts.
Blocking or locking: what is the difference?
Locking fault
The boiler stays stopped. The cause must be found and repaired before it runs again safely: this is when you need a technician.
Reminder (H codes)
H11, H12 and H13 do not stop the heating. They report a sensor to replace or a service date that has been reached.
What our customers say
Where do we work?
Our engineers repair and service Bosch boilers throughout Belgium, from Brussels to Wallonia and Flanders. Give us a call: we tell you right away when someone can come.
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The brands we work with
Our technicians work on all brands: they install, service and repair appliances from the major manufacturers. For a new installation, we recommend the model that suits your home and budget.
We buy our equipment from all the major Belgian wholesalers and suppliers, including Facq, Van Marcke and Desco: genuine parts, quickly available.
Frequently asked questions
What does EA 227 mean on a Bosch boiler?
The boiler could not detect a flame during start-up. After the fourth attempt it locks out. Gas supply, electrodes, flue, air/gas ratio and gas valve are the usual suspects.
My Bosch shows E9: is it serious?
E9 means a temperature limiter or the flue gas safety device has tripped. The boiler protects itself from overheating: the cause (circulation, pump, dirty heat block) must be found before it is used again.
What does A1 mean?
The heating pump is not building up pressure in the circuit. The pressure, the valves, air in the boiler and the pump itself are inspected.
C4 is on the screen but the boiler works: why?
After running non-stop for a whole day, the boiler stops briefly for a safety test. It is not a fault.
What should I do when a code appears?
Write down the code and the number shown next to it, then call us. Restarting the boiler over and over does not repair it and can hide the real cause.
Do you also repair Junkers boilers?
Yes. Junkers boilers are made by Bosch and use the same codes. We work on both brands, old and new.
Your Bosch shows an error code?
Phone us or choose a time online: an engineer comes with the parts your boiler is most likely to need.