ACV
No Heat Demand Recognition
No hot water, burner does not start, but display is on and shows normal status
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Faulty ACV tank thermostat or sensor, Open circuit in demand wiring, Misconfigured setpoint or operating mode, Stuck relay on control board
How to Fix / Troubleshooting
Safety: Isolate power before working on thermostats or wiring.
- 1. Check setpoint: Verify that the DHW temperature setpoint on the ACV controller is above the actual tank temperature.
- 2. Operating mode: Ensure the unit is not in holiday, standby, or legionella-only mode that may prevent normal heating.
- 3. Thermostat/sensor test: Compare displayed tank temperature with an external thermometer. If the display shows much higher than actual, the sensor may be faulty and should be replaced.
- 4. External controls: If an external thermostat or BMS controls the heater, temporarily bypass it by bridging the demand terminals (if allowed) to see if the unit starts.
If the unit still does not fire with a clear demand, the control board output to the burner may be faulty and require professional diagnosis.
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Repair Difficulty
Medium
3/5
Required Part
Tank Thermostat / DHW Sensor
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