Ariston 23 Microgenus hot water problem

[Mr N]

I have a 23 Mffi Microgenus and the problem is with the Hot Water. It is fine for 2 minutes and then goes cold and then comes on hot again. this will continue all the time a hot tap is open.
I have read the instructions and the flow chart suggests it may be a flow switch. I thought I would ask some extra advice here before trying this.

 

[Rob]

Plate HE. Requires cleaning or replacing as it is full of iron ixides. System also needs flushing to prevent it happening again.

 

[Agile]

If its really fine for TWO MINUTES then it will not be primarily a blocked plate HE.

Perhaps its the sensor failing when hot or more likely a problem with the APS or venturi.

( I am feeling very annoyed about APSs on this model after wasting 25 min checking the two PCBs on one of these today! The APS had initially checked OK but was eventually found to be slow/never returning to the rest position. )

Tony

 

[chrishutt]

I'd check the temperature sensors first. They're relatively cheap and easy to replace.

 

[Agile]

Does anyone understand these boilers in detail?

All the ones I see step modulate on DHW which seems very crude for such a recent boiler. Just min to max gas rate!

Is this really correct?

Tony

 

[Gasguru]

There were several variants of the A23MFFI Eurocombi series. Some would step modulate and some were fully modulating. Perhaps it is the same with the Microgenus range. I have a list of all the different pcbs fitted to Aristons - all based on serial numbers - they do like to complicate things

Perhaps an out of calibration overheat stat? Occasional had this on other boilers. Easy to test.