Viessmann Vitodens 100-W fault 59: supply undervoltage

What Does Error 59 Mean?

In the cited Viessmann Vitodens 100-W heat-only instructions, fault 59 is a burner lockout associated with power-supply undervoltage. The service response is to check the mains supply and, if the fault recurs, investigate the fan path. The code does not justify an owner changing the fan or boiler electronics. Applies to: Vitodens 100-W heat-only boilers in the cited UK installation instructions This definition is limited to the United Kingdom Vitodens 100-W heat-only manual cited below. Viessmann fault meanings differ across Vitodens generations, combination boilers, Vitocal heat pumps, and control platforms. Owner-safe checks: Save fault 59 and the model label, note building-wide power symptoms and power-source changes, and leave the boiler connection untouched. Qualified technician: Live mains, boiler connection, fan, harness, control, combustion, and sealed-case checks require a qualified electrician or Viessmann heating engineer.