The room stats don't send the call for heat to the boiler, they operate the motor on the valve unit. When it fully opens, contacts in there send the call for heat to the boiler and turn it on.I did think of that but thought the wiring would be complicated, as you couldn't just common up the outputs from each roomstat and send to the boiler, as one roomstat would feed back and open all the other valves. But there's obviously a way round that, I assume double-pole roomstat, one pole to its valve, the other commoned up with the others
Sorry fixitflav, didn't realise you were just a diy'er like me. Yeah, hopefully some of the pro's will chime in shortlyI'm sure it would be legal, it's on the water side. I've never had a bypass valve and I'm just a DIY-er, but I'd be surprised if it's hard to set one up. Maybe experts on here can comment, and say if there's anything you need to bear in mind when selecting a valve.