At a recent job i was fitting a bathroom where the customer had got someone in to fit a towel rail for them. After he drained the system fitted the towel rail and filled back up the heating did not work, the guy wont answer his phone and i've been left to try and fix it . Going with what i'm being told the heating was off, the system drained, the work done and then filled back up but the guy never put the heating on to try it. Its an Ariston system boiler with 2 zone valves next to the boiler HW cylinder in same cupboard. I tried opening the ZV's manually to see if the pump runs but no joy. Why would this happen from draining theb filling again