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Discuss Heat pump low pressure in the Renewable Energy area at UKPlumbersForums.co.uk.

  1. SmokeyJ

    SmokeyJ GSR

    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
     
  2. Leezygeezer

    Leezygeezer GSR

    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?
     
  3. SmokeyJ

    SmokeyJ GSR

    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
     
  4. oz-plumber

    oz-plumber Plumber

    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.
     
  5. SmokeyJ

    SmokeyJ GSR

    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
     
  6. quality

    quality Plumber GSR

    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.
     
  7. Howsie

    Howsie Plumber

    Brine would imply it's a GS heat pump. 1+1=2. Job done.
     
  8. SmokeyJ

    SmokeyJ GSR

    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.
     
  9. quality

    quality Plumber GSR

    Make sure the out coil is clean as a whistle
     
  10. Worcester

    Worcester Plumber

    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
     
    • Like Like x 1
  11. quality

    quality Plumber GSR

    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
     
    • Like Like x 1
  12. Worcester

    Worcester Plumber

    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 ?
     
  13. Worcester

    Worcester Plumber

    Ps we have an A here sitting in our museum of oddities :)
     
    • Like Like x 1
  14. quality

    quality Plumber GSR

    Not a bad unit mechanically its just the control is pretty limited
     
  15. SmokeyJ

    SmokeyJ GSR

    Had a quick look today before she went to work. System working and up to temp.
    System is 5 years old and had no problems until a year and a half ago. It will typically cut out on low pressure about 3 times a month.
    Previous works seems to be magna clean and auto bypass and possible flush/cleaner (info pretty vague). She mentioned they said it was one of the dirtiest he's seen.
    Checked heat pump. Only About 800mm in front of unit to next door, rear ok. Mi's ask for 1500mm so not ideal.
    Coil pretty clean, fan ok, pcb connectors seemed ok.
    System seems to be circulating fine (flow shown through ufh manifolds). Up to pressure and no air. Cleaned magna clean, not much but quite large deposits rather than the average black sludge. Ran a manual defrost cycle and no issues was about 5°c outside at which point customer had to go to work.
    Said she'll call when it next occurs.
    Still unsure as to what could be causing low pressure as it is only intermittent. The front clearance/ unit
    positioning is not good, but it was trouble free for 3 years. Tempted to give this one a miss as really not in the know with heat pump fault finding. My experience with heat pumps is fitting a couple of ecodans to a spec and that was a couple of years ago. Will pop a couple of pics up.
     
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