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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.

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    Hi there,

    Looking for some help with an IDM terra 26s heat pump.

    It’s not kicking in at its minimum temperature and needs switched off and then back on (sometimes several times) to get the heat pump to fire away. Does anyone know of this problem?

    It has a strange electrical fault. IDM won’t reply to any emails and struggling to find someone with knowledge of these pumps.

    • CommentAuthorRobL
    • CommentTimeDec 21st 2022
    I don’t know that heatpump, but a quick google said it’s a twin compressor gshp for stage control. I think that means it’s on/off (not inverter) and two of them. What you describe sounds like a relay inside is failing. I’ve come across 2 likely fail modes - a relay may have burnt out, sometimes still making contact if you try again. Sometimes, for no obvious reason, cheap relays get ‘tired’ and after a few years don’t always mechanically change state when told to.

    A burnt out relay usually shows obvious plastic deformation, with any luck it is just socketted and can be swapped out. A ‘sticky’ one is more tricky, placing a magnet near it ‘helps’ it out, it needs replacing too. Do you want to investigate yourself ( turn everything off first, wait a minute, open carefully, inspect), or find somebody to fix?
    • CommentAuthorGreenPaddy
    • CommentTimeDec 21st 2022
    Hi Elliot,

    I vaguely recall working on a Terra 15kW twin about 8 years ago. It had little or no control established by the installer, and just ran till it tripped on over pressure. It didn't like that at all, not surprisingly. I seem to think it was a reasonably simple unit.

    I suspect you need an electrical or controls engineer, who could sus out the simple logic for the run demand, follow that control signal through the system from the stat, and see where it is interrupted. Could well be a faulty relay as per RobL. My guess is that many HP installers would know how to fit new unit, as a black box, but little knowledge of the internal controls.

    I've got a PDF of the Terra installation manual, though not much in it about the internal controls. I think I had to just puzzle it out at the time. If you ping me your email, I can send that to you, for what it's worth. The approximate translation from German is amusing.

    Haven't seen JonG here for a while but you might be able to contact him?
    • CommentAuthorrevor
    • CommentTimeDec 21st 2022
    Don't know anything about heat pumps but I assume it has an electric motor. If it is an capacitor start motor it could be the capacitor the fault you describe is commensurate with faulty capacitor sometimes work and sometimes not.
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