f l flashing ideal isar he24?

LF
flame failure
likely causes
warped ignition electrode failing to spark at correct ignition sequence [would explain loud bang]
normally caused by blocked condensate trap
ignition electrode needs replacing
ionization pins need upgrading
condition of combustion insulation needs checking
condensate trap & heat exchanger sump need cleaning
& testing for adequate drainage of condensate

manwithnoname
May 2011

Whatever suggestions that could be made are gas related, therefore you need a gas safe registered engineer to look at it.

Carefree
March 2011