Baxi 105e fault- barely any CH, HW little better. Ideas?

Unsure if this is 2 separate problems or just 1. Would love some help.

My rads have been almost cold for 10days now. Boiler is igniting but only for a few seconds. Temperature lights occasionally reach 40C, sometimes none show, usually 30C. If I open the hot water tap just enough to ignite the boiler I can get steaming hot water 50% of the time.(lights up to 70C) Other times or if I open the tap more, it’s lukewarm or stone cold.

Every 5-15 mins the ignition neon flashes for a few seconds.

Every 15-20mins the air flow monitor flashes for 2-15 seconds.

Plumber cleaned up the flame sensor and the boiler performance improved somewhat for ½ hr before returning to previous function.

He also checked the flue and found it clear and ok. (sorry don’t have the detail on what exactly was ok). Thermistos healthy.

He’s going to fit a new flame senor when it arrives but I’m a bit frazzled, cold and worried whether it will solve air flow issue?

He says if that fails his next move is to replace the pcb

Any ideas?

(The plumber says he’s never found a fault like it and not a baxi fan- and so perhaps less experienced with them??).

Appreciate any help