ACV
ACV Water Heaters Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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E01
Water heater does not ignite, the burner does not start, and the display shows E01.
Ignition Failure / No Flame Detected
E02
Water heater locks out with E02, and the burner stops shortly after an ignition attempt.
Flame Loss During Operation
E03
The display shows E03, and the water heater shuts down shortly after startup; the fan may run briefly.
Flue Gas / Air Pressure Fault
E04
The unit displays E04 and will not fire, often immediately after power-on.
Overheat / Safety Thermostat Tripped
E05
Display shows E05, burner does not start, fan may run briefly.
Flow Temperature Sensor Fault (NTC Open/Short)
E06
Display shows E06, unit may run briefly then shut down, domestic hot water temperature unstable.
DHW Temperature Sensor Fault (NTC Open/Short)
E07
Display shows E07, unit shuts down, may be associated with very high temperature readings.
Return Temperature Sensor Fault / Overrange
E08
Display shows E08, unit does not start, fan may not run.
Fan / Combustion Air Blower Fault
E09
Display shows E09, burner does not ignite, may occur after long downtime.
Gas Valve / Gas Train Fault
E10
Display shows E10, unit shuts down, often associated with low system pressure on models with a sealed primary circuit.
Low Water Pressure / Low System Pressure
E11
Display shows E11, unit may run at reduced output or shut down intermittently.
Flow Switch / Flow Sensor Fault
E12
Display shows E12, unit may lock out, often associated with condensate issues on condensing models.
Condensate Drain / Level Fault
E13
Display shows E13, unit may shut down during operation, often with high flue temperature.
Flue Gas Temperature Too High / Flue Sensor Fault
E14
Display shows E14, unit does not respond to thermostat or control signals correctly.
Communication Fault (Control Board / Remote Panel)
E15
Display shows E15; unit may not respond to external demand (e.g., BMS or room thermostat).
External Control Input Fault
E16
Display shows E16; unit may run at limited power or shut down under high load.
Power Supply / Mains Voltage Fault
E17
Display shows E17; unit may shut down when the pump should be running.
Circulation Pump Fault (Primary Pump)
E18
Display shows E18; unit may overheat or cycle rapidly.
Flow Rate Too Low / Flow Sensor Differential Fault
E19
Display shows E19; unit may not modulate correctly or may shut down under high demand.
Modulation / Gas Valve Control Fault
E20
Display shows E20; unit may not start or may shut down randomly, often after power disturbances.
Internal Control Board Fault / EEPROM Error
Symptom
Condensate water dripping from the casing or joints instead of the drain pipe.
Condensate Leakage
Symptom
Corrosion or rust staining around connections on the stainless steel ACV tank.
Galvanic Corrosion / External Corrosion
Symptom
DHW recirculation loop not maintaining temperature, long wait for hot water at distant taps.
Recirculation Circuit Failure
Symptom
Frequent cycling of the burner with short on/off periods, even at steady demand.
Short Cycling
Symptom
Hot water runs hot then quickly goes lukewarm or cold during a shower.
Intermittent DHW Temperature / Short Draw Capacity
Symptom
Legionella protection cycle not completing or not reaching the required temperature.
Legionella Cycle Failure
Symptom
No hot water, burner does not start, and no error code is displayed.
No Power / Control Circuit Inactive
Symptom
No hot water, burner does not start, but the display is on and shows normal status.
No Heat Demand Recognition
Symptom
Smell of flue gases or combustion products near the water heater.
Flue Gas Leakage
Symptom
Smell of gas near the water heater, with no visible leak.
Gas Leak in Gas Train or Connections
Symptom
Water heater emits a rumbling or kettling noise during operation.
Scale Buildup in Heat Exchanger
Symptom
Water heater leaking from the bottom of the casing or around the base.
Tank or Heat Exchanger Leak
Symptom
Water heater leaking from the safety valve discharge pipe.
Overpressure / Safety Valve Discharge
Symptom
Water heater makes loud banging or knocking noises when the burner starts or stops.
Water Hammer / Expansion Noise
Symptom
Water heater vibrates excessively or the fan noise is very loud.
Fan Imbalance / Mounting Fault
Symptom
Water temperature too hot at taps, risk of scalding.
Overtemperature at Outlet
Symptom
Water temperature too low at taps, but the burner cycles normally.
Insufficient DHW Temperature / Capacity
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E01 |
Water heater does not ignite, the burner does not start, and the display shows E01.
|
Ignition Failure / No Flame Detected | View Details |
| E02 |
Water heater locks out with E02, and the burner stops shortly after an ignition attempt.
|
Flame Loss During Operation | View Details |
| E03 |
The display shows E03, and the water heater shuts down shortly after startup; the fan may run briefly.
|
Flue Gas / Air Pressure Fault | View Details |
| E04 |
The unit displays E04 and will not fire, often immediately after power-on.
|
Overheat / Safety Thermostat Tripped | View Details |
| E05 |
Display shows E05, burner does not start, fan may run briefly.
|
Flow Temperature Sensor Fault (NTC Open/Short) | View Details |
| E06 |
Display shows E06, unit may run briefly then shut down, domestic hot water temperature unstable.
|
DHW Temperature Sensor Fault (NTC Open/Short) | View Details |
| E07 |
Display shows E07, unit shuts down, may be associated with very high temperature readings.
|
Return Temperature Sensor Fault / Overrange | View Details |
| E08 |
Display shows E08, unit does not start, fan may not run.
|
Fan / Combustion Air Blower Fault | View Details |
| E09 |
Display shows E09, burner does not ignite, may occur after long downtime.
|
Gas Valve / Gas Train Fault | View Details |
| E10 |
Display shows E10, unit shuts down, often associated with low system pressure on models with a sealed primary circuit.
|
Low Water Pressure / Low System Pressure | View Details |
| E11 |
Display shows E11, unit may run at reduced output or shut down intermittently.
|
Flow Switch / Flow Sensor Fault | View Details |
| E12 |
Display shows E12, unit may lock out, often associated with condensate issues on condensing models.
|
Condensate Drain / Level Fault | View Details |
| E13 |
Display shows E13, unit may shut down during operation, often with high flue temperature.
|
Flue Gas Temperature Too High / Flue Sensor Fault | View Details |
| E14 |
Display shows E14, unit does not respond to thermostat or control signals correctly.
|
Communication Fault (Control Board / Remote Panel) | View Details |
| E15 |
Display shows E15; unit may not respond to external demand (e.g., BMS or room thermostat).
|
External Control Input Fault | View Details |
| E16 |
Display shows E16; unit may run at limited power or shut down under high load.
|
Power Supply / Mains Voltage Fault | View Details |
| E17 |
Display shows E17; unit may shut down when the pump should be running.
|
Circulation Pump Fault (Primary Pump) | View Details |
| E18 |
Display shows E18; unit may overheat or cycle rapidly.
|
Flow Rate Too Low / Flow Sensor Differential Fault | View Details |
| E19 |
Display shows E19; unit may not modulate correctly or may shut down under high demand.
|
Modulation / Gas Valve Control Fault | View Details |
| E20 |
Display shows E20; unit may not start or may shut down randomly, often after power disturbances.
|
Internal Control Board Fault / EEPROM Error | View Details |
| – |
Condensate water dripping from the casing or joints instead of the drain pipe.
|
Condensate Leakage | View Details |
| – |
Corrosion or rust staining around connections on the stainless steel ACV tank.
|
Galvanic Corrosion / External Corrosion | View Details |
| – |
DHW recirculation loop not maintaining temperature, long wait for hot water at distant taps.
|
Recirculation Circuit Failure | View Details |
| – |
Frequent cycling of the burner with short on/off periods, even at steady demand.
|
Short Cycling | View Details |
| – |
Hot water runs hot then quickly goes lukewarm or cold during a shower.
|
Intermittent DHW Temperature / Short Draw Capacity | View Details |
| – |
Legionella protection cycle not completing or not reaching the required temperature.
|
Legionella Cycle Failure | View Details |
| – |
No hot water, burner does not start, and no error code is displayed.
|
No Power / Control Circuit Inactive | View Details |
| – |
No hot water, burner does not start, but the display is on and shows normal status.
|
No Heat Demand Recognition | View Details |
| – |
Smell of flue gases or combustion products near the water heater.
|
Flue Gas Leakage | View Details |
| – |
Smell of gas near the water heater, with no visible leak.
|
Gas Leak in Gas Train or Connections | View Details |
| – |
Water heater emits a rumbling or kettling noise during operation.
|
Scale Buildup in Heat Exchanger | View Details |
| – |
Water heater leaking from the bottom of the casing or around the base.
|
Tank or Heat Exchanger Leak | View Details |
| – |
Water heater leaking from the safety valve discharge pipe.
|
Overpressure / Safety Valve Discharge | View Details |
| – |
Water heater makes loud banging or knocking noises when the burner starts or stops.
|
Water Hammer / Expansion Noise | View Details |
| – |
Water heater vibrates excessively or the fan noise is very loud.
|
Fan Imbalance / Mounting Fault | View Details |
| – |
Water temperature too hot at taps, risk of scalding.
|
Overtemperature at Outlet | View Details |
| – |
Water temperature too low at taps, but the burner cycles normally.
|
Insufficient DHW Temperature / Capacity | View Details |
No matching codes found
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