Ferroli Optima 701 problem

[rcw600]

This boiler is 12 years old. DHW is working OK but CH has intermittent problem with cutting out/cutting back in very frequently (every few seconds) usually with buzzing of the relays on the PCB (mainly relay 4). From what I've read here and in other forums online it looks most likely this is a PCB failure, but I'd appreciate any other opinions, e.g could it be one of the temp sensors or APS? This is the 4th problem I've had with it and I was planning to replace it this year, but I'd really like to get through the winter! PCB replacement looks like an easy job (if not cheap!).

Separately - any thoughts on the best replacement? Boiler engineer recommended another Ferroli but I am not so sure given the probs I've had with this one.

Thanks