Valiant thermostat , BMU-Err ?
Vaillant ecotec 937?
vaillant ecoTEC plus boiler fault code - how to fix?
resetting thermostatat?
Why is heating on at night?
Vaillant VCW-Sine18 T3WFH Lights but then goes off after 5 Min?
No hot water, intermittent when air temp drops?
Vaillant ecotec plus 630?
how do I rectify the fault as detailed below?