probably to late but ... starts itself & shoots up to 85? very common fault on these is the flow sensor not protected by scale reducer & sticks on. The boiler is off, but the flow sensor still fires up the boiler on max modulation. This causes boiler to boil , excess pressure & steam then cause the 8 o rings on the Hex's to leak. Exess heat (steam) from main hex travels down cold water in pipe & distorts (melts sometimes) the inners of the flow switch.
Intermittent lock out- could be caused by the above but . . - no one has suggested removing the restrictor ring from the flue. Its actually between the fan & recouperator. Installer often doesnt bother check to see if correct one fitted. How long is the flue? is it vertical?
Maybe all this has been checked & I suspect you are all sorted now. The comment about TRV is very true. The MI state it must have a bypass valve fitted but I bet it hasn't. It probably wasnt range rated either. Probably been took out the box hung on the wall switched on & left.
Intermittent lock out- could be caused by the above but . . - no one has suggested removing the restrictor ring from the flue. Its actually between the fan & recouperator. Installer often doesnt bother check to see if correct one fitted. How long is the flue? is it vertical?
Maybe all this has been checked & I suspect you are all sorted now. The comment about TRV is very true. The MI state it must have a bypass valve fitted but I bet it hasn't. It probably wasnt range rated either. Probably been took out the box hung on the wall switched on & left.
