from personally exp i have found it to be the pcb on most occasions with the no flame detection symbol.
Have tried all the other options of checking the gas valve, all the solenoids but most of the time we have found it to be pcb
depending on which model of britony if its the all white version they are prone to pcb. if you say the lock down as in the red light with the no flame symbol as long as its the all white version i would say its more than likely the pcb for that problem
90% pcb they had a series of faults with these and the age is about right for it.
If you phone up chaff they will check all the gas valve etc but from experience we have found them to be the pcb. which also comes with a new panel as well if its the mx range.
We fit at least 3 ariston clas he combi's 30kw a week.
nice boiler and now they do a 35kw i think it is now.
had a few set up issues but that has been engineers error more than boiler.
just cause he is corgi registered doesnt mean that engineers no everything about gas appliances and can fault find on the spot. the problem with most combi boilers is one fault that appears could be upto 3 or 4 different problems and tbh with the lower price range of boilers at the minute it is...
so you have to pay an extra 550 quid and the grant is for 2700 so some one is getting that for just changing the boiler surely they must be doing more than that.