Another Fortic question

[dennyboy]

what could cause a fortic to overflow with very hot water? - it happened overnight - the ballvalve is working fine, the overflow is taking water away no problem, so there must have been a lot of water in a short space of time, the water on the hot-taps was scalding in the morning, but the cylinder stat seemed to turn the boiler on and off when needed, the lad didnt check the pump and theres no immersion on it, he drained it down and re-filled it and ran the heating and hot water (potteron envoy) and everything seemed fine and has been for the last couple of days - there was a heating engineer out to the envoy the day before but apparently all he did was change the pcb - any ideas chaps, thanks

 

[ChrisR]

Leaking ball (float) valve?
Leaking coil inside ?

 

[dennyboy]

Ball-valve was fine (I changed that a few weeks back)
the f+e tank in the loft wasnt passing water
there is a mixer tap on the bath but this is fairly new
they did have a shower pump fitted? - but this had been disconnected and plumbing put back as it was
there was a heating engineer out to the boiler the day before but the householder said they only changed the board
the cylinder stat was turning off the boiler no probs
it was as if overnight the header tank on the fortic had a massive surge of boiling water that the overflow coulndt cope with?
oh and the immersion has been dissconected
the last one I come across like this was indeed a split coil but that wasnt scalding hot water
many thanks