ACV
ACV Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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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 run briefly then stop
Flue Gas / Air Pressure Switch Fault
E04
Boiler locks out with E04, no heating or hot water, temperature rises quickly before shutdown
Overheat Thermostat Trip / Safety High Limit
E05
Boiler displays E05 and will not start, often after a power cut or wiring work
Flow Temperature Sensor Fault (NTC Open/Short)
E06
Boiler shows E06, domestic hot water temperature is erratic or boiler will not fire for DHW
DHW Temperature Sensor Fault (NTC Open/Short)
E07
Boiler displays E07, fan may not start or runs briefly then stops
Fan Fault / Fan Speed Feedback Error
E08
Boiler shows E08, no heating or hot water, pump may not run.
Circulation Pump Fault
E09
Boiler locks out with E09, often accompanied by a rapid temperature rise on the display.
Flow Sensor / Flow Switch Fault (No Circulation Detection)
E10
Boiler shows E10, no operation, pressure gauge reads low or zero.
Low Water Pressure Lockout
E11
Boiler displays E11; the pressure gauge appears normal, but the boiler will not run.
Water Pressure Sensor / Switch Fault
E12
Boiler shows E12, no ignition, often after wiring changes or a power surge.
Communication Error Between Control Board and User Interface
E13
Boiler displays E13, burner stops, and may be associated with flue issues.
Flue Gas Temperature Overheat
E14
Boiler shows E14; DHW temperature overshoots, or the boiler cycles rapidly on hot water.
DHW Overtemperature / Anti-Scald Protection
E15
Boiler displays E15, no burner operation, often after condensate issues.
Condensate Drain Fault / Blocked Trap
E16
Boiler shows E16, burner does not start, and may be linked to external safety devices.
External Safety Circuit Open (e.g., Safety Thermostat, Limit Switch, Cascade Control)
E17
Boiler displays E17, with no response to the room thermostat or controller.
Room Thermostat / OpenTherm Communication Fault
E18
Boiler displays E18; burner output is limited, or the boiler shuts down under high demand.
Excessive Flow Rate / DHW Flow Sensor Fault
E19
Boiler displays E19; burner output is reduced, and the error may be logged as a sensor discrepancy.
Flow/Return Temperature Sensor Mismatch
E20
Boiler displays E20; there is no ignition, and the error may be associated with ionization current issues.
Flame Detection Circuit Fault
E21
Boiler displays E21; burner output is limited, and the error may be linked to an excessively high return temperature.
Excessively High Return Temperature / Low Delta-T
E22
Boiler displays E22; there is no burner operation, and the error may occur after power disturbances.
Internal Control Board Error
E23
Boiler displays E23; the burner stops, and the error may be associated with a low flue gas recirculation margin.
Combustion Fault / CO₂ Out of Range
E24
Boiler displays E24; there is no burner operation, and the error may be linked to a flue sensor or safety chain issue.
Flue Safety Device / Spillage Sensor Fault
E25
Boiler displays E25; burner output is limited, and the error may be associated with sensor calibration.
Sensor Calibration / Parameter Error
Symptom
Boiler display is blank or intermittent, but the power supply is present.
User Interface / Display Board Failure
Symptom
Boiler does not produce hot water, but heating works normally (combi or system with tank-in-tank).
DHW Priority / Diverter Fault
Symptom
Boiler frequently loses pressure and needs topping up.
Chronic Pressure Loss
Symptom
Boiler frequently short cycles (starts and stops every few minutes).
Short Cycling / Oversized Boiler or Control Issue
Symptom
Boiler is leaking water from underneath the casing.
Internal Water Leak
Symptom
Boiler makes loud banging or knocking noises (kettling) during operation.
Heat Exchanger Kettling / Localized Boiling
Symptom
Boiler produces hot water, but central heating does not work (combi or system).
Heating Circuit Isolation / Diverter Fault
Symptom
Boiler trips the electrical breaker or blows fuses when starting.
Electrical Short or Overcurrent
Symptom
Domestic hot water temperature fluctuates between hot and cold.
Unstable DHW Temperature Control
Symptom
Radiators are not heating properly, but the boiler appears to run.
Poor Heating Circuit Circulation
Symptom
The boiler does not respond to the room thermostat; heating stays off.
No Heat Demand from Controls
Symptom
The boiler emits a burning smell or plastic smell during operation.
Overheating Electrical Component or Dust Burn-Off
Symptom
The boiler fan runs, but the burner does not ignite, and no error code is displayed.
Ignition Sequence Incomplete
Symptom
The boiler flue terminal shows white staining or dripping condensate on the wall.
Condensate Management / Flue Termination Issue
Symptom
The boiler is very noisy (whistling, roaring, or droning) when firing.
Combustion Noise / Resonance
Symptom
The boiler runs continuously and does not turn off when the room is warm.
Heating Demand Stuck On
Symptom
The boiler runs, but hot water flow is weak compared to cold taps.
Reduced DHW Flow Rate
| 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 run briefly then stop
|
Flue Gas / Air Pressure Switch Fault | View Details |
| E04 |
Boiler locks out with E04, no heating or hot water, temperature rises quickly before shutdown
|
Overheat Thermostat Trip / Safety High Limit | View Details |
| E05 |
Boiler displays E05 and will not start, often after a power cut or wiring work
|
Flow Temperature Sensor Fault (NTC Open/Short) | View Details |
| E06 |
Boiler shows E06, domestic hot water temperature is erratic or boiler will not fire for DHW
|
DHW Temperature Sensor Fault (NTC Open/Short) | View Details |
| E07 |
Boiler displays E07, fan may not start or runs briefly then stops
|
Fan Fault / Fan Speed Feedback Error | View Details |
| E08 |
Boiler shows E08, no heating or hot water, pump may not run.
|
Circulation Pump Fault | View Details |
| E09 |
Boiler locks out with E09, often accompanied by a rapid temperature rise on the display.
|
Flow Sensor / Flow Switch Fault (No Circulation Detection) | View Details |
| E10 |
Boiler shows E10, no operation, pressure gauge reads low or zero.
|
Low Water Pressure Lockout | View Details |
| E11 |
Boiler displays E11; the pressure gauge appears normal, but the boiler will not run.
|
Water Pressure Sensor / Switch Fault | View Details |
| E12 |
Boiler shows E12, no ignition, often after wiring changes or a power surge.
|
Communication Error Between Control Board and User Interface | View Details |
| E13 |
Boiler displays E13, burner stops, and may be associated with flue issues.
|
Flue Gas Temperature Overheat | View Details |
| E14 |
Boiler shows E14; DHW temperature overshoots, or the boiler cycles rapidly on hot water.
|
DHW Overtemperature / Anti-Scald Protection | View Details |
| E15 |
Boiler displays E15, no burner operation, often after condensate issues.
|
Condensate Drain Fault / Blocked Trap | View Details |
| E16 |
Boiler shows E16, burner does not start, and may be linked to external safety devices.
|
External Safety Circuit Open (e.g., Safety Thermostat, Limit Switch, Cascade Control) | View Details |
| E17 |
Boiler displays E17, with no response to the room thermostat or controller.
|
Room Thermostat / OpenTherm Communication Fault | View Details |
| E18 |
Boiler displays E18; burner output is limited, or the boiler shuts down under high demand.
|
Excessive Flow Rate / DHW Flow Sensor Fault | View Details |
| E19 |
Boiler displays E19; burner output is reduced, and the error may be logged as a sensor discrepancy.
|
Flow/Return Temperature Sensor Mismatch | View Details |
| E20 |
Boiler displays E20; there is no ignition, and the error may be associated with ionization current issues.
|
Flame Detection Circuit Fault | View Details |
| E21 |
Boiler displays E21; burner output is limited, and the error may be linked to an excessively high return temperature.
|
Excessively High Return Temperature / Low Delta-T | View Details |
| E22 |
Boiler displays E22; there is no burner operation, and the error may occur after power disturbances.
|
Internal Control Board Error | View Details |
| E23 |
Boiler displays E23; the burner stops, and the error may be associated with a low flue gas recirculation margin.
|
Combustion Fault / CO₂ Out of Range | View Details |
| E24 |
Boiler displays E24; there is no burner operation, and the error may be linked to a flue sensor or safety chain issue.
|
Flue Safety Device / Spillage Sensor Fault | View Details |
| E25 |
Boiler displays E25; burner output is limited, and the error may be associated with sensor calibration.
|
Sensor Calibration / Parameter Error | View Details |
| – |
Boiler display is blank or intermittent, but the power supply is present.
|
User Interface / Display Board Failure | View Details |
| – |
Boiler does not produce hot water, but heating works normally (combi or system with tank-in-tank).
|
DHW Priority / Diverter Fault | View Details |
| – |
Boiler frequently loses pressure and needs topping up.
|
Chronic Pressure Loss | View Details |
| – |
Boiler frequently short cycles (starts and stops every few minutes).
|
Short Cycling / Oversized Boiler or Control Issue | View Details |
| – |
Boiler is leaking water from underneath the casing.
|
Internal Water Leak | View Details |
| – |
Boiler makes loud banging or knocking noises (kettling) during operation.
|
Heat Exchanger Kettling / Localized Boiling | View Details |
| – |
Boiler produces hot water, but central heating does not work (combi or system).
|
Heating Circuit Isolation / Diverter Fault | View Details |
| – |
Boiler trips the electrical breaker or blows fuses when starting.
|
Electrical Short or Overcurrent | View Details |
| – |
Domestic hot water temperature fluctuates between hot and cold.
|
Unstable DHW Temperature Control | View Details |
| – |
Radiators are not heating properly, but the boiler appears to run.
|
Poor Heating Circuit Circulation | View Details |
| – |
The boiler does not respond to the room thermostat; heating stays off.
|
No Heat Demand from Controls | View Details |
| – |
The boiler emits a burning smell or plastic smell during operation.
|
Overheating Electrical Component or Dust Burn-Off | View Details |
| – |
The boiler fan runs, but the burner does not ignite, and no error code is displayed.
|
Ignition Sequence Incomplete | View Details |
| – |
The boiler flue terminal shows white staining or dripping condensate on the wall.
|
Condensate Management / Flue Termination Issue | View Details |
| – |
The boiler is very noisy (whistling, roaring, or droning) when firing.
|
Combustion Noise / Resonance | View Details |
| – |
The boiler runs continuously and does not turn off when the room is warm.
|
Heating Demand Stuck On | View Details |
| – |
The boiler runs, but hot water flow is weak compared to cold taps.
|
Reduced DHW Flow Rate | View Details |
No matching codes found
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