I have the same 'issue' here - I had currently latched the valve open and would now prefer to connect to the pump as suggested but my pump is internal to a Vaillant system boiler and I'm not entirely sure the best way to connect it. If you figure it out please let us know! I don't want to go back to the S plan since I had the same as you - on numerous occasions the OT bridge fired the boiler with no zone valve open which inevitably resulted with the bypass overheating and the boiler cycling...