Update to this, on site for last 2 days checking everything.
This cylinder is now turned off, aswel as the problem above the two port valve was getting a feed back from a underfloor manifold that had an other mains feed to it from a separate distribution board and a switch live back to main junction box, when that underfloor called for heat the 2 port for the unvented cylinder opened and would not have shut even when the thermal cut out operated!
In another area a Unihub tank in tank thermal store, basicly a thermal store with an unvented cylinder inside had no combinded thermostat/ thermal cut out in the unvented cylinder because the pipework had been fitted over the pocket, at the bottom of the store is another pocket that is supposed to have a stat set at 40c for the underfloor to be run from, this is where the thermostat/ thermal cut out had been fitted. Incorrectly installed D1 pipework.
another area another unvented with incorrectly installed d1 pipework.
All three systems are supposed to be controlled by one of these
http://www.radiantcontrol.co.uk/wp-content/uploads/2010/05/d360e.pdf with a mixer valve, not one even wired only a very expensive read out for the outside temp.
All either made safe or turned off untill defects sorted out.
Will post some pics tomorrow
