Glow-worm
Glow-worm Furnaces Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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F1
Furnace locks out with F1 displayed; burner does not ignite.
Ignition lockout / ignition failure
F10
F10 displayed; furnace fails to start, no response from user controls.
Communication fault between user interface and main PCB
F11
F11 error: The furnace runs, but central heating does not get hot, or temperature control is erratic.
Flow Sensor / Pump Feedback Fault
F12
F12 displayed: The furnace locks out intermittently, often during high demand.
Gas Valve Control Fault
F13
F13 error: The furnace shuts down with signs of overheating in the flue area.
Flue Gas Temperature Overheat
F14
F14 displayed: The furnace will not start after a power interruption or wiring changes.
External Control / Thermostat Input Fault
F15
F15 error: The furnace display shows low system pressure and locks out.
Low Water Pressure / Pressure Sensor Fault
F16
F16 displayed: The furnace locks out with signs of rapid temperature rise.
Pump Overrun / Circulation Fault
F17
F17 error: The furnace fails to ignite or burns with an unstable flame.
Gas Supply / Gas Rate Fault
F18
F18 displayed: The furnace shuts down with an electrical smell or no response.
Mains Supply / Polarity / Earthing Fault
F19
F19 error: The furnace display flickers or resets randomly.
Low Voltage / Power Supply Instability
F2
Furnace shows F2 and shuts down shortly after ignition attempt.
Flame detection failure / flame signal lost
F20
F20 displayed: The furnace overheats and locks out frequently.
Primary Circuit Flow Restriction / Overheat
F3
F3 displayed; furnace overheats and shuts down, may be noisy before lockout.
Primary heat exchanger overheat / high limit thermostat trip
F4
Furnace displays F4 and will not start; fan does not run.
Fan / air pressure system fault
F5
F5 error; furnace attempts to start but shuts down quickly, fan may run continuously.
Air pressure switch / flue proving fault
F6
F6 displayed; furnace cycles on and off rapidly or fails to modulate correctly.
Flow temperature sensor fault
F7
F7 error; furnace may overheat quickly or show incorrect temperature readings.
Return temperature sensor fault
F8
F8 displayed; furnace locks out during operation, may be associated with hot water demand on combi-style furnace/boiler units.
Domestic hot water temperature sensor fault (on DHW-equipped Glow-worm furnaces/boilers)
F9
F9 error; furnace will not fire, may occur after power surge or wiring work.
PCB / internal control fault
Symptom
Furnace causes lights to dim or trips the breaker when starting.
High inrush current / electrical fault
Symptom
Furnace condensate pipe dripping heavily or leaking inside the casing.
Condensate drainage fault
Symptom
Furnace cycles on and off frequently; rooms never reach the set temperature.
Short cycling / control mismatch.
Symptom
Furnace display works, but controls are unresponsive or buttons do not function.
User interface keypad failure
Symptom
Furnace emits a whistling or high-pitched noise during operation.
Gas flow resonance / fan or flue noise.
Symptom
Furnace fan runs, but the burner does not light, and no error code is shown.
Ignition sequence interruption
Symptom
Furnace flue terminal shows staining or soot marks on the wall.
Incomplete combustion / flue gas spillage
Symptom
Furnace frequently loses pressure; the user has to top up the system often.
Chronic pressure loss / leak.
Symptom
Furnace locks out more often during very cold weather, accompanied by gurgling sounds.
Frozen or restricted condensate / air in heat exchanger
Symptom
Furnace makes loud banging or knocking noises when starting or stopping.
Kettling / water hammer in heat exchanger.
Symptom
Furnace runs but no domestic hot water; radiators heat normally (combi-style Glow-worm furnace/boiler).
DHW priority / flow detection fault.
Symptom
Furnace runs but no heat to radiators; pipes near the furnace are hot, but radiators stay cold.
Circulation failure / valve issue.
Symptom
Furnace runs but radiators only get warm at the top, and cold at the bottom.
Sludge accumulation in radiators.
Symptom
Furnace runs continuously and overheats the house, even when the thermostat is turned down.
Control stuck on / thermostat failure
Symptom
Furnace smells of burning plastic or electrical burning.
Overheating electrical component.
Symptom
Furnace smells of gas around the casing or nearby.
Gas leak at appliance.
Symptom
Furnace starts then shuts down after a few seconds; radiators are lukewarm.
Flame instability / poor combustion
Symptom
Furnace will not start, no lights or display, completely dead.
No power to appliance.
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| F1 |
Furnace locks out with F1 displayed; burner does not ignite.
|
Ignition lockout / ignition failure | View Details |
| F10 |
F10 displayed; furnace fails to start, no response from user controls.
|
Communication fault between user interface and main PCB | View Details |
| F11 |
F11 error: The furnace runs, but central heating does not get hot, or temperature control is erratic.
|
Flow Sensor / Pump Feedback Fault | View Details |
| F12 |
F12 displayed: The furnace locks out intermittently, often during high demand.
|
Gas Valve Control Fault | View Details |
| F13 |
F13 error: The furnace shuts down with signs of overheating in the flue area.
|
Flue Gas Temperature Overheat | View Details |
| F14 |
F14 displayed: The furnace will not start after a power interruption or wiring changes.
|
External Control / Thermostat Input Fault | View Details |
| F15 |
F15 error: The furnace display shows low system pressure and locks out.
|
Low Water Pressure / Pressure Sensor Fault | View Details |
| F16 |
F16 displayed: The furnace locks out with signs of rapid temperature rise.
|
Pump Overrun / Circulation Fault | View Details |
| F17 |
F17 error: The furnace fails to ignite or burns with an unstable flame.
|
Gas Supply / Gas Rate Fault | View Details |
| F18 |
F18 displayed: The furnace shuts down with an electrical smell or no response.
|
Mains Supply / Polarity / Earthing Fault | View Details |
| F19 |
F19 error: The furnace display flickers or resets randomly.
|
Low Voltage / Power Supply Instability | View Details |
| F2 |
Furnace shows F2 and shuts down shortly after ignition attempt.
|
Flame detection failure / flame signal lost | View Details |
| F20 |
F20 displayed: The furnace overheats and locks out frequently.
|
Primary Circuit Flow Restriction / Overheat | View Details |
| F3 |
F3 displayed; furnace overheats and shuts down, may be noisy before lockout.
|
Primary heat exchanger overheat / high limit thermostat trip | View Details |
| F4 |
Furnace displays F4 and will not start; fan does not run.
|
Fan / air pressure system fault | View Details |
| F5 |
F5 error; furnace attempts to start but shuts down quickly, fan may run continuously.
|
Air pressure switch / flue proving fault | View Details |
| F6 |
F6 displayed; furnace cycles on and off rapidly or fails to modulate correctly.
|
Flow temperature sensor fault | View Details |
| F7 |
F7 error; furnace may overheat quickly or show incorrect temperature readings.
|
Return temperature sensor fault | View Details |
| F8 |
F8 displayed; furnace locks out during operation, may be associated with hot water demand on combi-style furnace/boiler units.
|
Domestic hot water temperature sensor fault (on DHW-equipped Glow-worm furnaces/boilers) | View Details |
| F9 |
F9 error; furnace will not fire, may occur after power surge or wiring work.
|
PCB / internal control fault | View Details |
| – |
Furnace causes lights to dim or trips the breaker when starting.
|
High inrush current / electrical fault | View Details |
| – |
Furnace condensate pipe dripping heavily or leaking inside the casing.
|
Condensate drainage fault | View Details |
| – |
Furnace cycles on and off frequently; rooms never reach the set temperature.
|
Short cycling / control mismatch. | View Details |
| – |
Furnace display works, but controls are unresponsive or buttons do not function.
|
User interface keypad failure | View Details |
| – |
Furnace emits a whistling or high-pitched noise during operation.
|
Gas flow resonance / fan or flue noise. | View Details |
| – |
Furnace fan runs, but the burner does not light, and no error code is shown.
|
Ignition sequence interruption | View Details |
| – |
Furnace flue terminal shows staining or soot marks on the wall.
|
Incomplete combustion / flue gas spillage | View Details |
| – |
Furnace frequently loses pressure; the user has to top up the system often.
|
Chronic pressure loss / leak. | View Details |
| – |
Furnace locks out more often during very cold weather, accompanied by gurgling sounds.
|
Frozen or restricted condensate / air in heat exchanger | View Details |
| – |
Furnace makes loud banging or knocking noises when starting or stopping.
|
Kettling / water hammer in heat exchanger. | View Details |
| – |
Furnace runs but no domestic hot water; radiators heat normally (combi-style Glow-worm furnace/boiler).
|
DHW priority / flow detection fault. | View Details |
| – |
Furnace runs but no heat to radiators; pipes near the furnace are hot, but radiators stay cold.
|
Circulation failure / valve issue. | View Details |
| – |
Furnace runs but radiators only get warm at the top, and cold at the bottom.
|
Sludge accumulation in radiators. | View Details |
| – |
Furnace runs continuously and overheats the house, even when the thermostat is turned down.
|
Control stuck on / thermostat failure | View Details |
| – |
Furnace smells of burning plastic or electrical burning.
|
Overheating electrical component. | View Details |
| – |
Furnace smells of gas around the casing or nearby.
|
Gas leak at appliance. | View Details |
| – |
Furnace starts then shuts down after a few seconds; radiators are lukewarm.
|
Flame instability / poor combustion | View Details |
| – |
Furnace will not start, no lights or display, completely dead.
|
No power to appliance. | View Details |
No matching codes found
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