Viessmann [E6] fault codewhat it means and how to fix it

E6 is one of the few Viessmann codes with a householder remedy printed against it. The first-generation Vitodens 100 and 100-W WB1A gives "E6 — Burner blocked — Water pressure too low — Top up water", the 2008 WB1B installation instructions carry the same row, and the Vitotronic-controlled 200-W B2HA and 242-F B2UA read "Burner blocked — System pressure too low — Top up with water." The control unit reads a pressure sensor in the primary circuit and refuses to fire below the minimum; because the burner is blocked rather than locked out, it starts again on its own once pressure is restored, so there is no reset. What changes by unit is whether you see a code at all. The 2011 WB1B service instructions, the WB1C, B1HA and B1HC tables and the 050-W BPJD have no E6: on those the operating instructions say the system pressure reading flashes on the display instead, and the B1HC operating instructions give 0.8 bar as the minimum.

The householder instruction comes from Viessmann's WB1A operating instructions: low system water pressure is shown flashing, contact your heating engineer, and "it is possible to recharge the system via the filling loop", with the warning that care must be taken to ensure the fill valve is not left turned on. The Vitotronic operating instructions are more reserved, telling the owner to ask the heating contractor for the required system pressure and the position of the shut-off valves, so on a 200-W or 242-F the steps below apply only if your installer has shown you the filling loop. A system that needs topping up more than once or twice a year is losing water somewhere, and that is the contractor's. On the 2020-on numeric-table units the equivalent is F.74 (system pressure too low), which stops both the burner and the pump; F.87 is pressure too high and F.471 a pressure sensor fault.

1. 1

   Read the pressure gauge with the boiler cold. On the B1HC-generation 100-W Viessmann give 0.8 bar as the minimum; on other units ask your installer for the figure, and take a note of the reading before you do anything.

2. 2

   If your installer has shown you the filling loop, open its valves slowly until the gauge reaches the pressure they set, then close both valves fully. Viessmann's own warning: care must be taken to ensure the fill valve is not left turned on. The burner restarts by itself once pressure is back.

   If you have not been shown the filling loop, or the pressure drops again within days, stop and call your heating contractor. Repeated topping up hides a leak and wears the boiler.