The boiler has been in bits again. Turns out the refurbished PCB unit is also faulty and worse than the one we took out.
It worked fine for a few days but then this morning refused to fire up leaving us with no heat or hot water and no amount of cajoling would coax it back into life.
So we had no option but to swap it back for the one that produces heat and hot water but needs resetting on a regular basis.
The "new" one will have to go back again.