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Heat pump low pressure

Discuss Heat pump low pressure at UK Plumbers Forums; Hi all After checking jobs for the week I see the office have booked me in to a customer who has a Danfoss DHP-AX heat pump. She has had ongoing ...
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    Default Heat pump low pressure

    Hi all
    After checking jobs for the week I see the office have booked me in to a customer who has a Danfoss DHP-AX heat pump. She has had ongoing problems with the unit cutting out and displaying 'low pressure' error. Another company has tried to fix (only info is - replaced filters, altered pipework etc) and no further to resolving fault. She did mention to her knowledge they have not checked the external unit...
    My experience with heat pumps is limited and I don't do the refrigeration side. We have an air con engineer on firm who can check the refrige side. I am just wondering if anyone has come across this problem before? Am I right in thinking it would be better suited for the air con engineer to attend and check refrige pressures, low pressure switch etc. Or is there an external factor that can influence this issue that I can check i.e flow problems?
    I don't like going out to heat pumps with not doing refrigeration as it seems you can only do half a job.
    Thanks Jason

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    Default Re: Heat pump low pressure

    Low pressure trips can be a number of faults, has it been like this ever since it was installed? If so, is it correctly positioned?

    If the fault is intermittent, it is not likely to be a loss of refrigerant gas as it would be constantly tripping out. Any other fault symptoms accompanying the low pressure trips?

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    Default Re: Heat pump low pressure

    Have not been to site yet so unsure of any other symptoms or history.
    Only info i have is from an email 'I have a danfoss DHP-AX, The system cuts out when low pressure error shows on the display panel. I spent just £1000 with a company who seemed to replace filters and added a bit of extra piping etc... They never checked the unit outside and never fixed the problem'
    Apologies if i'm sounding daft , so it could be various things that could cause fault. Only external factors i can think would be airflow or circulation based issues or am i missing something? All other factors would be related to the refrige side? Just makes sense to me to get the refrige checked at the same time so i may save chasing my tail if it is say a faulty low pressure switch. Or am i taking the wrong approach

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    Default Re: Heat pump low pressure

    What is the low pressure error referring to?

    Refrigerant side or water side.

    It's probably something you should find out from the customer prior to attending the property.



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    Default Re: Heat pump low pressure

    I am assuming it's the low pressure on the compressor side. Don't see a mention of a low pressure switch on the water side in the manual. In the trouble shooting guide there is loads of things to check. It mentions various checks on the 'brine' circuit. Have not heard of a 'brine' circuit before, is this just another wording for the heating system

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    Default Re: Heat pump low pressure

    We look after an estate in Leeds with about 30 AX air source heat pumps. They are not the most efficient unit but they are pretty reliable refrigeration wise. Its worth checking the connectors within the internal control panel as I have a good few with both high and low pressure errors being down to a bad connection on the plugs on the PCB a squeeze with a pair of pliers does the trick.

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    Default Re: Heat pump low pressure

    Quote Originally Posted by SmokeyJ View Post
    I am assuming it's the low pressure on the compressor side. Don't see a mention of a low pressure switch on the water side in the manual. In the trouble shooting guide there is loads of things to check. It mentions various checks on the 'brine' circuit. Have not heard of a 'brine' circuit before, is this just another wording for the heating system
    Brine would imply it's a GS heat pump. 1+1=2. Job done.

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    Default Re: Heat pump low pressure

    Quality - Thanks I'll give them a check.
    Howsie - I was wondering but I'm sure its a ashp, thinking troubleshooting guide in manual may be a bit generic. Manual I have is for the dhp-ax ashp.

    Main query was if it is likely to be a refrigerant or a water side issue. Seems that it could be either so I'll go have a look
    Work mate said it may cut out on low pressure when on defrost if it's not getting the temp rise from the heating?
    Going to site tomorrow so will get more of an understanding of what's going on.

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    Default Re: Heat pump low pressure

    Make sure the out coil is clean as a whistle

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    Default Re: Heat pump low pressure

    Some of the old Danfoss ASHP's were GSHP's with a brine (glycol filled) coil used as an air collector !!! Those are the Danfoss DHP-A and DHP-AX units

    The DHP-AQ units are the usual Monoblocs
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    Default Re: Heat pump low pressure

    No the DHP AX were their first true DX coil/Evaporator ASHP as opposed to the DHP A which was effectively a ground source unit with a glycol fan coil. The DHP AX are also mono block units
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    Default Re: Heat pump low pressure

    Thanks quality, happy to stand corrected, the manuals I have for the AX units have glycol circuits in them .... left hand not knowing what the right hand was doing ?
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