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  1. #1
    Senior Member Rank = Supreme Champion RS2OOO's Avatar
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    Inverter ASHP Operation and Settings (Thermotec)

    Recently got my 2nd hand 17kw inverter heat pump up and running.

    Can anyone confirm what settings to change to make it most suitable for the pond?

    I've changed a couple -
    R04 - Temp difference adjusted from 1C to 0.5C
    R10 - Min Heat adjusted from 15C to 10C

    Everything else is as per the whatever the previous owner or the factory set.


    Thing is, every time it runs it does so at the same compressor frequency (52hz), never any higher or lower. MikeH from here pointed out this is what you'd expect from a non-inverter on/off type machine which defeats the point of having an inverter - which should adjust the compressor frequency to maintain lower running costs and prevent constant stop/starting of the ASHP.

    Here's a screenshot to demonstrate (bottom chart):




    Could it be a setting somewhere that is causing this?

    I increased the pump flow rate yesterday to see if that changed anything but it didn't. (Pump is a 20k lph variable that was running at 52% and I increased to 70% but no change in compressor frequency at all.

    Any ideas?


    Last edited by RS2OOO; 24-05-2024 at 10:31 AM.

  2. #2
    Quote Originally Posted by RS2OOO View Post
    Recently got my 2nd hand 17kw inverter heat pump up and running.

    Can anyone confirm what settings to change to make it most suitable for the pond?

    I've changed a couple -
    R04 - Temp difference adjusted from 1C to 0.5C
    R10 - Min Heat adjusted from 15C to 10C

    Everything else is as per the whatever the previous owner or the factory set.


    Thing is, every time it runs it does so at the same compressor frequency (52hz), never any higher or lower. MikeH from here pointed out this is what you'd expect from a non-inverter on/off type machine which defeats the point of having an inverter - which should adjust the compressor frequency to maintain lower running costs and prevent constant stop/starting of the ASHP.

    Here's a screenshot to demonstrate (bottom chart):




    Could it be a setting somewhere that is causing this?

    I increased the pump flow rate yesterday to see if that changed anything but it didn't. (Pump is a 20k lph variable that was running at 52% and I increased to 70% but no change in compressor frequency at all.

    Any ideas?
    Total guess here RS - I left mine at a 1 Celsius temp difference and its ramps up and down as you’d expect. Because at 0.5 Celsius is such a small delta, could it be programmed to operate at a low frequency, so you only 52hz?

    Maybe try changing it to 1 Celsius and see if it ramps the hz up higher when it sees a bigger delta?


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  4. #3
    Senior Member Rank = Supreme Champion davethefish1's Avatar
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    odd one that mate as the inverter scales output to temperature differential.
    does the inverter alter compressor speed on frequency or something else 52hz is what mains 240 is at standard..?
    does the inverter run at higher htz than standard 52htz mains?

    have you got an energy monitor to see how many watts and amps it is using?

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  6. #4


    Had to reboot mine to get the info as the wifi keeps dropping. As you can see, mine ramps according to temp differential.

    Mine is the same as yours but the 12kw version Inverter ASHP Operation and Settings (Thermotec)


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  8. #5
    Senior Member Rank = Supreme Champion RS2OOO's Avatar
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    Thank you both for the replies, which I took on board for some experimenting.

    No matter what normal usage settings I changed, it would only operate at 52hz with no variation.

    So I changed values of H06 (Minimum heating frequency) and H36 (Start Frequency) to 65hz and sure enough it operated at 65hz which gave some piece of mind that the inverter board is not entirely bricked.

    Once I normalised these settings it then went back to operating at 52hz.

    Temp difference was indeed set to 0.5C (target temp 19C), so instead of changing that I turned ASHP off for a while and let temp drop to sub 19C, then turned it back on with a new target temp of 20.5 to create a larger differential between current temp and target temp.

    After doing that the ASHP did kick in at 62hz, then gradually dropped to 52hz. All future runs since then have been at 52hz again.


    So it does seem that my 0.5C temp differential is a factor causing it to run at 52hz, but I have at least proven that when more demand is placed on the ASHP it will ramp up to a faster operating frequency, thus it appears to be working correctly.

    I still don't understand why it won't run lower than 52hz - maybe since our electrical supply is naturally at that level it would be less efficient for it to convert it to a lower speed?
    I thought it would run longer at a lower frequency to maintain temp and avoid having to switch on/off constantly which increases component / compressor wear.

    Either way, I've at least proven the inverter board is capable of increasing frequency when the demand is present.

    On top of all this because the ASHP is grossly oversizsed for my pond, it can probably just tick over at the normal supply frequency to achieve what it needs to do.
    Last edited by RS2OOO; 29-05-2024 at 01:44 PM.

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