Viessmann Error Codes & Diagnostics
Complete diagnostic directory for official Viessmann fault codes. Verify root causes, safe troubleshooting steps, and replacement part numbers before calling a technician.
Viessmann Vitodens 100-W fault 59: supply undervoltage
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.
Viessmann burner lockouts: what the fault checker can and cannot settle
A Viessmann burner lockout means the appliance attempted to establish combustion, failed to prove it within the permitted attempts, and stopped offering heat. Viessmann's own fault checker maps the displayed code to a condition, and the value of that tool is that it distinguishes lockouts from blocking faults, which behave and clear along different lines. Applies to: Viessmann Vitodens gas condensing boilers whose displayed fault codes are listed in the Viessmann fault checker The Vitodens range spans wall-hung combi, system, and floor-standing appliances across several generations, and code meanings are model-specific. Enter the code into Viessmann's own checker together with the appliance model rather than relying on a list that does not ask which boiler you have. Owner-safe checks: Photograph the display showing the code, then copy the full model name and serial number from the appliance data plate. | Record whether the boiler recovered on its own or needed a reset, and how many times each has happened. | Check the system pressure gauge while the system is cold and note the reading. Qualified technician: Gas pressure measurement, ignition and sensing component work, flue inspection, and condensate system correction are Gas Safe registered tasks. | A boiler that locks out again immediately after a reset should be left alone rather than reset repeatedly, because each attempt spends further ignition cycles against the same condition.