A20
Hoval
Mains supply / power module fault
Furnace indicates power supply fault or undervoltage, intermittent resets
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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
Low mains voltage, Loose supply terminals in Hoval control box, Defective power supply unit on control board, Shared circuit overloaded
How to Fix / Troubleshooting
Safety: Only qualified persons should work on live electrical circuits. Isolate power before tightening terminals.
- Check supply: Verify that the furnace is on a dedicated circuit with the correct voltage and breaker size as per Hoval documentation.
- Inspect terminals: Open the control box and check the L/N/PE terminals for tightness and signs of overheating.
- Remove overloads: Disconnect any non-approved devices sharing the furnace supply.
- Monitor voltage: If undervoltage is suspected from the utility, contact your electrician or supplier. Persistent errors may indicate a failing internal power supply module.
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Repair Difficulty
Hard
4/5
Required Part
Control Board Power Supply
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