I have spent a lot of time thinking about adding the following to my TT as we boondock a lot.
2 - Normally Closed, 12V solenoid valves (potable water and temp rated)
1 - Normally Open, 12V solenoid valve (potable water and temp rated)
1 - 12V Timer Relay (pulse activated) with at least 2 relays
1 - Push button (perhaps with LED)
Assorted pipe fittings
Assorted electrical connectors and wire
Install 1 NC valve under sink (between hot and cold supply) at furthest point from Water Heater. (In my case the kitchen sink)
Install 1 NC valve at water pump between water tank and pump inlet.
Install 1 NO valve in cold water line after the pump and after the line "Ts" off to supply the water heater. (This ones tricky to explain. You want to be able to interrupt the flow through the cold side, but still allow cold supply to water heater when the system is activated)
Install push button in convenient spot (you could install several in parallel such as kitchen and bath)
Wire in Timer Relay to sent current to all 3 Valves and to water pump.
Are you guys still with me?
The system when activated uses the existing cold supply lines as a return path for the hot side.
The pump will come on and draw water from cold supply line and pump it to the Water Heater forcing hot water through the valve (now open) at the kitchen sink.
The timer is adjusted for how ever long it takes currently to get hot water to the sink from a cold start.
One of the nice things is you only have to run wire and not water lines.
With a little more thought and modification you could use it to heat (carefully) your water tank in the winter.
All comments and critiques welcome.
Loulong, what did you use to draw your diagram?