Viessmann [50] fault codewhat it means and how to fix it

On a Vitodens with a cylinder — a 100-W or 200-W system boiler with an indirect cylinder, or a 111-W or 222-F storage combi, which has one built in — the control unit reads the stored water temperature through a cylinder temperature sensor. 50 is "No DHW heating — Short circuit, cylinder temperature sensor" and 58 is "No DHW heating — Lead break, cylinder temperature sensor", with the measure "Check the sensor". The system characteristic is the useful part: the boiler carries on heating the house and stops only the cylinder charging, because without a plausible cylinder temperature it cannot know when to stop. On the Vitotronic 200-W B2HB the row is widened to "cylinder temperature sensor or comfort sensor", the comfort sensor being the one in the plate heat exchanger of a combi variant.

The WB1B system boiler is the exception that proves the code is about the control unit rather than the boiler name. The 2018 edition of the WB1B installation instructions, for the 7.9 to 35 kW system and open-vent versions, gives 50 and 58 as "No DHW heating — Cylinder demand terminal box fault — Check terminal box connections and replace the terminal box if required": on that unit the cylinder is called for through a terminal box wired to an external cylinder thermostat, and the same two codes report that box rather than a sensor. On a 050-W BPJD, which is a combi only, neither code exists. There is no householder step beyond noting the code, and no reset is listed. On the 2020-on numeric-table units the pair is F.7 (lead break) and F.8 (short circuit) — note the order is the reverse of 50/58.