Hi

Is it possible to connect the output from a mains pressure hot water supply (Heated by a thermal store - solar + wood stove input with plate heat exchanger PX for the mains pressure side) to the input of a Puma combi gas boiler on the hot water side. The Puma manual states mains pressure cold water input, but if I turn down the hot water temperature output setting on the boiler to low (40-50C), and kept the mains pressure hot water input from the Thermal store PX to no more than 70C, would the combi not fire up until the temperature of out put dropped to <40C. The Combi has the std overheat stats in addition to the output hot water temp control stat.

Any thoughts

I wouldn't do it without checking first. I've read discussions that suggest some combi boilers will use cheaper plastic fittings on the 'cold' side, and these are not guaranteed to cope with hot water, particularly at mains pressure. You might also find that your boiler runs very inefficiently as it's not really designed to heat water up 'just a little' and will cycle too rapidly to make an efficient, clean burn.

The best bet would be to ring Puma directly and ask them, I doubt it would hurt and they might be able to advise you on the best set up. Could you get a thermal store with a three coil input and use the combi that way?

We're planning on going down the thermal store route, but still waiting on planning appeal so haven't got as far as detailed specifications. Annoyingly the boiler in our caravan packed up, and as it's a rare full sized model we've had to spend about a grand on replacing it. We might be able to take it into the house when it gets built as it's probably worth as much as the whole caravan is!