Chosen Solution
FERcondens 25 HE keeps flashing A 21 keeps flashing A 21 and no heating no hot water boiler will not fire
@patalun error code A21 is a poor combustion fault and it is generated by fault F20 generated 6 times in the last 10 minutes. Fault F20 is a Combustion control fault possible causes are: Fan fault to alleviate check the fan and fan wiring Wrong flue restrictor to alleviate check the flue restrictor and replace it Flue not correctly sized or obstructed to alleviate check the flue This should give you something to work with.
