Viessmann [E3] fault codewhat it means and how to fix it

E3 is "Burner in a fault state — Fault in safety chain" on the WB1C, B1HA/B1KA and B1HC/B1KC, the 111-W B1LA to B1LD and the 050-W BPJD. Viessmann's measures are "Check the temperature limiter and connecting leads. Check the control unit and replace if required." The safety chain is the series circuit through the temperature limiter that the burner control unit must see closed before it will run the burner; F2 is that limiter opening because the water got too hot, while E3 is the chain being open or implausible for another reason — a broken lead, a limiter that has failed open with the water cool, or the control unit input that reads it. The two rows sit next to each other in the table and are frequently confused. Neither is a minor sensor fault, and an earlier version of this page that described E3 as a flow temperature sensor problem was wrong; the correction is recorded in our research notes.

The scope is narrower than most two-character codes. The 2011 WB1B service instructions and the 2008 and 2018 WB1B installation instructions have no E3 row, and neither does the WB1A. On the 2020-on units with the numeric table the nearest rows are F.184 and F.185 (short circuit or lead break, flow temperature sensor/high limit safety cut-out) and, importantly, a bare "E 3" on the home screen of a B1HF, B1HG, B1GA or 111-W B1LF is not a fault at all — Viessmann's operating instructions say it means the holiday programme has been switched on through the ViCare app.

On a Vitotronic-controlled 200-W, 222-F or 242-F, E3 is a different fault entirely. That table reads "Burner in a fault state — Heat transfer too low during calibration. Temperature limiter has shut down." with the measures "Ensure adequate heat transfer. Check circulation pump for faults, scale or blockages. Press reset button R." It is a Lambda Pro combustion-controller code: the burner was running its ionisation-current calibration, the water could not carry the heat away, and the limiter stopped it. Same letters, a circulation problem rather than a wiring one, and a reset key rather than a rotary selector. There is no householder step for either E3 in any operating instructions we read: a reset on the unit's control is permitted once, and a recurrence is the contractor's.