Thermona
Thermona Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
Advertisements
E01
Boiler does not ignite, display shows E01 shortly after a heating or DHW demand.
Ignition Failure / No Flame Detection
E02
Boiler locks out with E02, burner stops shortly after ignition or during operation.
Flame Loss During Operation
E03
Boiler shows E03 and does not start, fan may not run or runs briefly then stops.
Flue Gas / Air Pressure Switch Fault
E04
Display shows E04, boiler shuts down and will not restart until reset.
Overheat Thermostat Trip
E05
Boiler displays E05 and does not fire, or fires briefly then shuts down.
Flow Temperature Sensor (NTC) Fault
E06
Boiler shows E06, domestic hot water (DHW) temperature is erratic or boiler will not fire for hot water.
DHW Temperature Sensor (NTC) Fault
E07
Boiler locks out with E07, no heating or hot water, fan may run continuously or not at all.
Fan / Fan Speed Feedback Fault
E08
Boiler shows E08, will not start, sometimes accompanied by loud humming from pump area.
Circulation Pump Fault
E09
Boiler displays E09, no heating or hot water, pressure gauge may read zero or very low.
Low Water Pressure / Pressure Switch Fault
E10
Boiler shows E10, pressure gauge indicates high pressure (often above 3 bar), safety valve may discharge water.
Overpressure / Expansion Fault
E11
Boiler intermittently locks out with E11, especially during hot water use, temperature fluctuates.
Flow Sensor / Turbine Fault (DHW Flow Detection)
E12
Boiler shows E12, no response to thermostat or control signals.
Communication Fault with Room Thermostat / Control Bus
E13
Boiler displays E13, burner stops, may be accompanied by unusual combustion noise.
Flue Gas Temperature Overlimit
E14
Boiler shows E14, no ignition, often after power disturbances or wiring work.
Gas Valve Control Fault
E15
Boiler intermittently shows E15, especially during rapid temperature changes or after long operation.
Return Temperature Sensor (NTC) Fault
E16
Boiler shows E16, burner shuts down, sometimes accompanied by gurgling noises in the heat exchanger.
Lack of Water Circulation / Flow Switch Fault
E17
Boiler displays E17, no heating, but hot water may still function (on combi models).
3-Way Diverter Valve Position Fault
E18
Boiler shows E18, no operation, often after power surges or lightning.
Internal Electronics / PCB Fault
E19
Boiler intermittently shows E19, especially when external sensors or weather compensation are connected.
External Sensor / Weather Compensation Fault
E20
Boiler shows E20, burner stops, may be associated with condensate issues on condensing models.
Condensate Drain / Siphon Fault
Symptom
Boiler condensate pipe drips or gurgles loudly, with occasional lockouts in cold weather.
Condensate Drainage / Freezing Issues
Symptom
Boiler cycles on and off rapidly (short cycling) without maintaining stable temperature.
Short Cycling / Oversized Boiler or Control Issue
Symptom
Boiler display is blank, no lights or response, but mains supply appears present.
No Power / Internal Fuse or PCB Failure
Symptom
Boiler does not respond to room thermostat, stays off even when there is a demand for heat.
Control Signal / Thermostat Fault
Symptom
Boiler emits a burning smell or visible smoke from the casing.
Electrical Overheating / Component Failure
Symptom
Boiler emits a strong gas smell around the appliance or flue area.
Gas Leak / Incomplete Combustion
Symptom
Boiler fan is very noisy, with whistling or grinding sounds during operation.
Fan Mechanical Wear / Flue Resonance
Symptom
Boiler frequently loses pressure and needs topping up every few days.
Chronic Pressure Loss
Symptom
Boiler frequently trips the electrical circuit breaker or blows fuses.
Electrical Short Circuit / Overcurrent
Symptom
Boiler ignites with a loud bang or pop (delayed ignition).
Delayed Ignition / Gas-Air Mixture Issue
Symptom
Boiler leaking water from underneath the casing or from pipe connections.
Internal Water Leak
Symptom
Boiler makes loud banging or knocking noises (kettling) during operation.
Heat Exchanger Kettling / Localised Boiling
Symptom
Boiler runs but radiators do not get hot, while domestic hot water works normally (combi models).
Heating Circuit Isolation / Diverter Valve Stuck on DHW
Symptom
Boiler runs continuously and overheats the property, even when thermostat is turned down.
Boiler Fails to Shut Down on Demand
Symptom
Domestic hot water temperature fluctuates between hot and cold during use.
Inconsistent DHW Temperature Control
Symptom
Radiators are only warm at the top or some radiators stay cold while others heat up.
Poor Circulation / Air in System
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E01 |
Boiler does not ignite, display shows E01 shortly after a heating or DHW demand.
|
Ignition Failure / No Flame Detection | View Details |
| E02 |
Boiler locks out with E02, burner stops shortly after ignition or during operation.
|
Flame Loss During Operation | View Details |
| E03 |
Boiler shows E03 and does not start, fan may not run or runs briefly then stops.
|
Flue Gas / Air Pressure Switch Fault | View Details |
| E04 |
Display shows E04, boiler shuts down and will not restart until reset.
|
Overheat Thermostat Trip | View Details |
| E05 |
Boiler displays E05 and does not fire, or fires briefly then shuts down.
|
Flow Temperature Sensor (NTC) Fault | View Details |
| E06 |
Boiler shows E06, domestic hot water (DHW) temperature is erratic or boiler will not fire for hot water.
|
DHW Temperature Sensor (NTC) Fault | View Details |
| E07 |
Boiler locks out with E07, no heating or hot water, fan may run continuously or not at all.
|
Fan / Fan Speed Feedback Fault | View Details |
| E08 |
Boiler shows E08, will not start, sometimes accompanied by loud humming from pump area.
|
Circulation Pump Fault | View Details |
| E09 |
Boiler displays E09, no heating or hot water, pressure gauge may read zero or very low.
|
Low Water Pressure / Pressure Switch Fault | View Details |
| E10 |
Boiler shows E10, pressure gauge indicates high pressure (often above 3 bar), safety valve may discharge water.
|
Overpressure / Expansion Fault | View Details |
| E11 |
Boiler intermittently locks out with E11, especially during hot water use, temperature fluctuates.
|
Flow Sensor / Turbine Fault (DHW Flow Detection) | View Details |
| E12 |
Boiler shows E12, no response to thermostat or control signals.
|
Communication Fault with Room Thermostat / Control Bus | View Details |
| E13 |
Boiler displays E13, burner stops, may be accompanied by unusual combustion noise.
|
Flue Gas Temperature Overlimit | View Details |
| E14 |
Boiler shows E14, no ignition, often after power disturbances or wiring work.
|
Gas Valve Control Fault | View Details |
| E15 |
Boiler intermittently shows E15, especially during rapid temperature changes or after long operation.
|
Return Temperature Sensor (NTC) Fault | View Details |
| E16 |
Boiler shows E16, burner shuts down, sometimes accompanied by gurgling noises in the heat exchanger.
|
Lack of Water Circulation / Flow Switch Fault | View Details |
| E17 |
Boiler displays E17, no heating, but hot water may still function (on combi models).
|
3-Way Diverter Valve Position Fault | View Details |
| E18 |
Boiler shows E18, no operation, often after power surges or lightning.
|
Internal Electronics / PCB Fault | View Details |
| E19 |
Boiler intermittently shows E19, especially when external sensors or weather compensation are connected.
|
External Sensor / Weather Compensation Fault | View Details |
| E20 |
Boiler shows E20, burner stops, may be associated with condensate issues on condensing models.
|
Condensate Drain / Siphon Fault | View Details |
| – |
Boiler condensate pipe drips or gurgles loudly, with occasional lockouts in cold weather.
|
Condensate Drainage / Freezing Issues | View Details |
| – |
Boiler cycles on and off rapidly (short cycling) without maintaining stable temperature.
|
Short Cycling / Oversized Boiler or Control Issue | View Details |
| – |
Boiler display is blank, no lights or response, but mains supply appears present.
|
No Power / Internal Fuse or PCB Failure | View Details |
| – |
Boiler does not respond to room thermostat, stays off even when there is a demand for heat.
|
Control Signal / Thermostat Fault | View Details |
| – |
Boiler emits a burning smell or visible smoke from the casing.
|
Electrical Overheating / Component Failure | View Details |
| – |
Boiler emits a strong gas smell around the appliance or flue area.
|
Gas Leak / Incomplete Combustion | View Details |
| – |
Boiler fan is very noisy, with whistling or grinding sounds during operation.
|
Fan Mechanical Wear / Flue Resonance | View Details |
| – |
Boiler frequently loses pressure and needs topping up every few days.
|
Chronic Pressure Loss | View Details |
| – |
Boiler frequently trips the electrical circuit breaker or blows fuses.
|
Electrical Short Circuit / Overcurrent | View Details |
| – |
Boiler ignites with a loud bang or pop (delayed ignition).
|
Delayed Ignition / Gas-Air Mixture Issue | View Details |
| – |
Boiler leaking water from underneath the casing or from pipe connections.
|
Internal Water Leak | View Details |
| – |
Boiler makes loud banging or knocking noises (kettling) during operation.
|
Heat Exchanger Kettling / Localised Boiling | View Details |
| – |
Boiler runs but radiators do not get hot, while domestic hot water works normally (combi models).
|
Heating Circuit Isolation / Diverter Valve Stuck on DHW | View Details |
| – |
Boiler runs continuously and overheats the property, even when thermostat is turned down.
|
Boiler Fails to Shut Down on Demand | View Details |
| – |
Domestic hot water temperature fluctuates between hot and cold during use.
|
Inconsistent DHW Temperature Control | View Details |
| – |
Radiators are only warm at the top or some radiators stay cold while others heat up.
|
Poor Circulation / Air in System | View Details |
No matching codes found
Advertisements