how can i fix my ariston bolier, model microgenus 24 HE?

This is probably the answer to your problem. I had the same thing with the flame sensor. I made a video and posted it to youtube, it's easy and only cost me 3p to repair. https://www.youtube.com/watch?v=u-L3PzGQAa4

Clive Hancy
November 2016

PS that boiler comes up with error codes when it fails, mine failed with A01.

You haven't specified what code it fails with, the code is displayed on the boiler readout, the meaning can be found in the booklet left by your installer or on the ariston microgenus HE PDF, found on their website :-)

Beaks
October 2009

I'm not a plumber/heating engr but i've had this fault on the same boiler, i cured it by replacing the main PCB (£95 ish).

Took about 20-30 mins with mains off.

Fault is supposedly caused by flame sensor failing, the common excuse being the spark is going down the flame sensor and damaging the components on the main board, some say bending the LHS electrode away from the other 2 may cure this. Time will tell.

The good news is replacing the PCB fixed my problem, the bad news is, i'm an electronics engr and i can't find the fix for the board on the net, but resistors and transformers don't sound like the fault to me (because the fault is intermittent and these components are either faulty, or not, but nothing in between.)

Hopefully some more knowledgeable engr will provide which components are supposedly failing and save us all a fortune.

Beaks
October 2009