i've got a Halstead Quattro combi, a couple of months ago the diverter valve went, so we had someone out to replace it, while he was there he also replaced the PCB because it wasn't firing up properly. Worked fine for a while, then last night, running the hot tap to wash up, the overheat lockout light came on. Pressing the reset button didn't fix it, turning it off overnight then trying again this morning didn't make a difference. Pressure was low so I topped it up with the feeder valve, still as soon as a hot tap is turned on, the red light comes on. Any ideas?