Viessmann No Power to Appliance

Water heater will not power on, display is blank

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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

Tripped circuit breaker or blown fuse, Faulty external isolation switch, Loose power terminal block in heater, Failed internal fuse on main PCB

How to Fix / Troubleshooting

Safety: Before opening the unit, confirm power is off at the breaker. Use a voltage tester if available.

  • Check supply: Verify that the dedicated breaker is on and that any external fused spur has an intact fuse.
  • Inspect power cable: Ensure the power cord or fixed wiring to the heater is not damaged.
  • Check internal terminals: Remove the electrical cover and confirm that L, N, and PE connections are tight.
  • Internal fuse: Some Viessmann boards have an internal fuse. If accessible, check and replace only with the specified type. If it blows again, a deeper fault exists and requires a technician.
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Repair Difficulty

Medium 3/5

Required Part

Internal PCB Fuse
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