CampinGazz used his keyboard to write :
i'm fitting a home style heating and water system to my motorhome, a 12 volt
eberspacher 5KW water boiler, a 20 litre twin coil calorifier (hot water
cylinder with an extra coil to heat from the engine) 3 radiators, digital
programmer, tank and room stats, and hopefully a 3 way valve to select hot
water, heating or both to be heater when the boilers running.

12v 5Kw sounds to be rather a large supply cable (?)


But i just can't seem to find a 12 volt DC powered 3 way valve, the mid
position type that's fitted to 99% of home central heating systems,

You might have better luck finding a pair of simple 12v solenoid valves
instead of the three port.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk