Ariston Microgenus 23 MFFI intermittent hot water

[sonaldo]

so i have an Ariston Microgenus 23 MFFI boiler in the house i recently moved into. just for context i maintain the boiler pressure around 1.0 bar

recently the hot water has become intermittent. i timed it earlier:
- i turned the shower on, the boiler fired up
- it heated teh water for a minute then switched off
- 2min 15secs later it tried to fire again, but failed
- then there was a 'whirring' noise after 2m 45secs
- it fired again after 3m 20 secs, but went off again
- then again at 3m 30 secs before going off again

- 5 mins after, i turned off shower and turned back on again
- it fired then went off after 10 secs
- then fired again before immediately switching off
- whirring noise again after 30 secs
- then fired again at 2m 20 secs
- then it stayed on

we seem to be able to get it to work after having this back and forth for 5 or so minutes, but clearly something's wrong

for what it's worth the central heating works fine. we don't have it on at the moment, but when i manually switch it on the boiler fires and stays fired

got a guy coming round this week. he said it might be temperature sensor or something else small, but might also be the heat exchanger which would be costly to replace. he reckons it might be time for a new boiler

if anyone has any views would be interesting to hear