Boiler start sequence only on HW demand

[tvrjohn]

Having problems with a 28 CDI combi, and would like some ideas on what is the specific solution PLEASE

Central heating stops working and 'domestic hot water demand indicator - flashing fast red light.

ok Manual says its Air Flow Fault (RSF)
checked fan flue, looks ok


sparks and lights burner to supply hot water demand, but will not start with heating demand request

Is this a control problem ?

 

[adlplumbing]

where in lancshire are you not sure of problem but if your in bolton area i can come out have look no fix no fee