What is the best solution to my 3 way valve question: I am setting up a Solcrafte mains pressure (no pump!) batch solar heater 150L to feed during the hotter months the taps directly or preheat the cold supply to a AUER Edel Air heat pump with 100L tank. I have found thermostatic diversion valves sets such as ESBE VMD300 (3 way thermostatic divertor + 3 way thermostatic valve) which can be set to let >45C bypass the heat pump and go directly to the taps <45C water go to the heat pump. The heat pump will accept up to 65C via the "cold" supply and the divertor. The hot from the solar heater (max 95C) thus needs tempering with a 3 way thermostatic valve set to mix to 65C. The question I have if I stop and drain the solar there would be no water pressure (or hot water) at the hot inlet of the 3 way valve. Would the valve work to let just the cold water through? If it did not, what solution would you suggest?