Bosch Boiler Error Codes — Greentherm & Greenstar Fault Guide
Fault code reference for Bosch Greentherm and Greenstar condensing boilers. EA, C1, C6, A3, and F2 codes — what they mean and how to respond as a BC homeowner.
Understanding Bosch Boiler Fault Codes
Bosch Greentherm and Greenstar condensing boilers use an alphanumeric fault code system displayed on the unit's front panel. Codes are categorised by prefix:
- EA codes — ignition and flame-related lockout faults. These always lock out the boiler and require investigation before resetting.
- C codes— sensor and combustion system faults. These typically lock out the boiler and require a technician's diagnostic tools.
- A codes — advisory faults. A3 (low pressure) locks out the boiler; A1 (maintenance due) is a reminder only and the boiler continues to operate.
- F codes — safety-critical faults (overheat). These lock out the boiler and should not be reset without identifying the root cause.
- E codes — environmental/mechanical faults such as condensate drain issues.
It is also worth noting that Bosch Greenstar boilers share platform architecture with Worcester Bosch products in certain product generations. If you have a unit with Worcester Bosch branding but similar error codes, the same diagnosis approach applies.
If you smell gas at any point when your boiler displays a fault code, do not reset. Evacuate, call FortisBC at 1-800-663-9911, and wait for clearance before re-entering.
Bosch Error Code Reference Table
Covering Bosch Greentherm and Greenstar series condensing boilers for the Canadian market. Code labels may vary slightly by firmware version.
| Code | Name | Meaning | Common Cause | DIY Check? | Urgency |
|---|---|---|---|---|---|
| EA 224 | Ignition Failure — No Flame | The boiler attempted ignition and failed to establish a flame within the trial period. | Failed igniter electrode, gas valve not opening, low gas pressure, or combustion air issue. | Partial — verify gas supply to other appliances, attempt single reset. Repeat lockout requires a technician. | High |
| EA 227 | Ignition Failure — Flame Signal | Ignition was attempted but the control board did not receive a valid flame signal. | Dirty or cracked flame sensor electrode, incorrect electrode gap, or intermittent gas supply. | No — flame sensor inspection and gap measurement required. | High |
| EA 229 | Repeated Ignition Failure (Lockout) | The boiler has made repeated ignition attempts and entered a hard lockout state. | Cumulative ignition fault — underlying cause (gas valve, electrode, or pressure) not resolved. | No — root cause investigation required before reset. | High |
| EA 338 | Safety Chain Open | One of the safety interlock devices (overheat stat, pressure switch, LWCO) has interrupted the control circuit. | Overheating, low water pressure, or faulty safety device causing a nuisance trip. | No — each safety component must be tested individually to identify the open contact. | High |
| C1 | Flue / Exhaust Sensor Fault | The flue gas temperature sensor is reading out of range or reporting a fault condition. | Sensor failure, wiring fault, or genuine high flue gas temperature from scale buildup. | No — sensor resistance testing and combustion analysis required. | Moderate to High |
| C6 | Fan / Combustion Air Fault | The combustion fan is not operating within the expected speed range during pre-purge. | Fan motor bearing wear, partially obstructed fan wheel, or failed capacitor. | No — fan speed measurement and motor inspection required. | High |
| A3 | Low Water Pressure | System water pressure has dropped below the minimum operating threshold. | Expansion tank bladder failure, slow system leak, or auto-fill valve not maintaining pressure. | Partial — check pressure gauge on the boiler. If above 0.5 bar, try re-pressurising. If pressure drops again, call a technician. | Moderate |
| F2 | Overheat / High Temperature Limit | The boiler has exceeded the high-temperature safety setpoint. | Low system flow, seized circulator pump, closed zone valves, or heat exchanger scaling. | No — investigate flow restriction before resetting. Do not repeatedly reset F2. | High |
| A1 | Maintenance Due / Service Reminder | The annual maintenance interval has been reached. Boiler continues to operate. | Service timer has reached the programmed interval set at last commissioning. | Yes — this is a reminder. Schedule annual service with a certified technician. | Low |
| E9 | Condensate / Drainage Fault | The condensate drain path is restricted or blocked, preventing normal condensate removal. | Frozen condensate pipe in cold weather, blocked condensate trap, or kinked drain hose. | Partial — inspect accessible condensate drain for freezing or blockage. Thaw with warm water only. | Moderate |
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