Which faults are common on Viessmann boilers?
Viessmann is a German manufacturer, and its Vitodens wall-hung condensing boilers are the models you are most likely to have at home in Birmingham. They report faults with a short code on the display. Viessmann describes most of the homeowner-facing codes the same way: “burner in a fault state”, followed by the reason.
No flame (F4). The most common Viessmann code. The boiler tried to light but saw no flame signal. Viessmann’s service instructions list the ignition and ionisation electrode, the gas pressure, the gas train and the condensate drain among the checks. For a homeowner, that means checking the gas supply first and, in frost, the condensate pipe outside. Our boiler won’t fire up guide and frozen condensate pipe guide take you through it.
Overheat (F2). The temperature limiter has tripped. Viessmann’s own checks begin with the system fill level, the pump and venting the system. In practice, low pressure or trapped air is often behind it, so check the gauge and bleed the radiators. If it returns, the pump or the limiter needs an engineer. See boiler keeps switching off and boiler losing pressure.
Fan and control faults (F9, Fd). F9 means the fan did not reach the right speed when the burner started; Fd is a fault in the burner control unit. Neither can be fixed safely from outside the boiler.
Flame at the wrong time (F3). If a flame signal is detected before the burner should have lit, the boiler stops for safety. This is a job for an engineer.
Servicing a Viessmann boiler
A yearly service by a Gas Safe registered engineer covers the burner, the electrodes, the heat exchanger, the condensate trap and the flue. Keep the record, as manufacturer warranties normally require it. See boiler servicing.
When should you get an engineer?
A burner fault has a cause that repeated resets will not fix. Reset once after the basic checks. If the code returns, or it is F3, F9 or Fd, send an enquiry with the model and code. A local Gas Safe registered engineer will diagnose the fault and give a price before any work starts.