Tools needed: Torx T20, fine sandpaper or steel wool, multimeter with microamps.
A loose or damaged wire between the main control board and an external sensor (like an outdoor temperature sensor) can trigger this lockout. viessmann d6 error
Because this error involves the combustion and venting system, repairs involving the fan, gas valves, or internal components should be performed by a Gas Safe registered engineer Tools needed: Torx T20, fine sandpaper or steel