| Main Display Code | Fault | Possible Solution | Resources |
|---|---|---|---|
| 10,11,12,13,14 | Sensor fault S1 Flow switch does not disconnect | • Check wiring for break • Replace S1 • Check flow switch | |
| 20,21,22,23,24 | Sensor fault S2 | • Check wiring for break • Replace S2 | |
| 0 | Sensor fault after self check | • Replace S1 and/or S2 | |
| 1 | Temperature too high | • Air in installation • Pump not running • Unsufficient flow in installation, radiators closed, pump setting too low • Flow switch sticking | |
| 2 | S1 and S2 interchanged | • Check cable loom • Replace S1 or S2 | |
| 4 | No flame signal | • Gas tap closed • No or incorrect ignition gap • Gas supply pressure too low of failling • Gas valve or ignition unit not powered | |
| 5 | Poor flame signal | • Condensate drain blocked • Check adjustment of gas valve | |
| 6 | Flame detection fault | • Replace ignition cable + spark plug cap • Replace ignition unit • Replace boiler controller | |
| 8 | Incorrect fan speed | • Fan catching on casing • Wiring between fan and casing • Check wiring for poor wire contact • Replace fan* | |
| 29,30 | Gas valve relay faulty | • Replace boiler controller |
Gas work stays with a Gas Safe registered engineer. Some codes only apply to a named range — check the model column.