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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthormartinlta
    • CommentTimeSep 28th 2007 edited

    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
    • CommentAuthortony
    • CommentTimeSep 28th 2007
    We dont know but it might work. A lot of combi boilers dont 'know' about warm water coming in as they are not expecting that so cant cope electronically.

    Try it an see and let us know how you get on. In a few years time they will all be advertising it as a feature but we are ahead of the times here.
    • CommentAuthorTuna
    • CommentTimeSep 28th 2007
    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!
    • CommentAuthormartinlta
    • CommentTimeSep 28th 2007
    I have also thought it may not be good for the combi boiler, and have a second design that uses 2 solenoid valves and a separate flow switch to bypass the combi boiler if the thermal store is hot enough. Note the thermal store is not pressurised only the mains water side of the plate heat exchanger.
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