I have two supplies into a new horstman e7 box, 1 from the offpeak water heating one from standard tariff boost do both suppies go to 1 and 2, 4 &5 linked, when wired this way boost RCBO trips ,if I remove the off peak it works albeit no off peak I fitted 2 new RCBO boards a while back but there has been a DIY joinery effort at boxing everything in since