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Blue Light Indication |
Lockout reset button |
Fault | Possible solution/check |
Off | Off | No power at control board | Permanent mains supply to boiler. Boiler mains switch. Fuse F1, 2.5A or Fuse F3, 0.5A Transformer (both coils below 100Ω). Otherwise replace control board. |
On | Off |
Boiler not operating during central heating demand (HW ok) Boiler operating without live demand at ST10-LR (from external roomstat timer). Boiler not operating during hot water demand (CH ok). Boiler not operating during any demand. |
External diverter valve. External timer or room stat OR if optional diverter valve is fitted: Temperature control in frost protection position. Live demand at ST-10-LR (external CH demand). Facia mounted timer if fitted. Diverter valve. Control board. Some older thermostats (containing capacitors) may give a low voltage return at ST10-LR when the thermostat contacts are open. Check that there is not a permanent live at ST10-LR from another source. External diverter valve. External timer or cylinder stat OR if optional diverter valve is fitted: Short circuit across ST8 from cylinder stat/timer. Facia mounted timer if fitted. Diverter valve. Control board Temperature control in frost protection position. Live demand at ST10-LR (from external system). Control board. OR if optional diverter valve is fitted: Timer. Control board. |
Slow flash (normally off, flashes on) | Flashing (reset required) | Ignition lockout | Gas present and at correct pressure. Combustion CO2 level. Flue condition. Ignition electrodes / harness / connections. Gas valve (coils 140-190Ω) / low voltage harness connection. Otherwise replace control board. |
Slow flash (normally on, flashes off) | Flashing (reset required) |
Flue overheat Heat exchanger overheat Flue blockage |
Heat exchanger blocked. Heat exchanger baffles removed and not refitted. Water pressure. All air vented. Pump / harness / connections. Water leaks / blockages. Safety thermostats / low voltage wiring harness / connections. Otherwise replace control board. Blockage in flue system. |
Fast flash | Off | Volatile lockout | Temperature sensor (8000-20,000Ω). Low voltage wiring harness / connections to sensor. Fan / fan harness / connections to fan. Code plug fitted. |
Fast flash | Flashing | Internal fault | Replace control board |
2 pulses | No light | Not a fault code | Service mode selected to min, press service button to return to normal. |
5 pulses | No light | Not a fault code | Service mode selected to max, press service button to return to normal. |