With full UFH you can remove jumper 3!
This will also help to identify or eliminate an overheating issue as the flow temp will be reduced to 63°C.
Could be that it needs to run at 75C as DHW is also incorporated in the thermal store, as most are. Reducing the boiler flow temperature to 76C or even better reducing the store temp to say 70-72C and always having boiler just set to 2C above store setpoint may solve it.
Good advice about the pump overrun, but from what I read this is a newish problem?
I am not familiar with the Barcelona (well not these days as there are so few left after frustrated scrapping), but does it need the pump switch from the boiler?
If this pump was switched independently from the store's stat I would have put an overrun on from new. I would also have put on two stats with latching relay to prevent boiler cycling.
The problem is when the new pcb was fitted. This may be just poor contacts somewhere, or is the existing thermister compatible with the new pcb? Or have many problems surfaced at the same time?
The problem is repairable, as the Promax is basically the same boiler. People just get ****ed off with continually ironing out the faults and downtime and then scrap it.
Lets face it, if this boiler only does long burns and does not cycle as it is is on a store, a cheap simple BIASI or Heatline would do the job just as well as any other boiler. The anti-cycling control of the store ensures minimum wear of the boiler parts and longevity. But, Broags are high quality and well priced (may not last for long if they take off), so their range is very appealing price, quality and spec wise.
I would be inclined to fit a Broag boiler using a 3-way diverter valve and have Surrey flange on the UFH flow pipe to the store. When DHW is called the boiler ramps up and sends 80C water the top of the store for DHW, when satisfied the diverter valve sends weather compensated low temperatures to the bottom of the store for UFH. The stat(s) may have to be moved up into the DHW section and a be a clamp on version.
AFAIK, thermal store compatibility on the Barcelona pcb was just having a fixed rate burner and modulation disabled.