I have a solar hot water system that thermocycles the hot water to the roof every night - a previous similar problem with thermocycling hot water to the central heating system was resolved by fitting an automatic stop valve wired to the central heating pump which creates a full shut off when the timer stops the pump. Before going the expense and technical challenge of working out where and how to replicate a similar valve in the roof panel circuit I wonder if anyone else has encountered this issue and if so how was it resolved.