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Daikin heating and circulating water when no demand

Steve W

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55 minutes ago, ProDave said:

Is this another "need to keep the compressor warm" type of issue?  Similar to Mitsubishi where some models have a sump heater

Was wondering this.

Can you tell how much power the unit is drawing when it is set to 15⁰C?

Should not be as much as the proper inbuilt water heater.

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1 hour ago, Steve W said:

After a significant amount of digging it appears that if the water temperature drops below 15C that the unit has real problems in cold weather. The optional backup is heater is not so optional especially during defrost cycles. 


Can Daikin Altherma be delivered without a backup heater?
No. The backup heater must be installed to ensure that the water temperature never drops below 59ºF (15ºC) during startup of the system or during defrost.


This was in the FAQ for North America.


@Steve W can you tell us how it copes with holidays? Can you turn the HP right off or does it keep the water heated to 15C even then, and how long does it take to get going from cold? Also could you say which model number you have got as they have several different ranges.


I have been looking at Daikin because they advertise their high temperature HPs as drop-in boiler replacements, but this min temp seems to be quite a limitation!


I was also pleased to read about your Tado setup, in the light of experience is there anything you would do differently? It certainly supports my plan to keep our Honeywell wireless zone valves and existing UFH zone controls, with the rads calling for the higher temp via a volt-free contact similar to your regime.

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Yes, this is a hidden gotcha. I couldn't work out why in scheduled mode there wasn't an OFF and that the lowest temperature was 15C. The net effect is that you are paying for the pump and also heating the water in the loop. As my water temperature is set to 45C it would circulate water at 35C whether the unit was on or off! After the visit from Daikin the temperature was adjusted and now it tends to be just the pump. This ASHP seems to have all manner of quirks which means that 95% of the time it is fine and the other 5% I may as well switch it off.

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  • 3 weeks later...

I've got exactly this issue on my ASHP which I'm raising with Daikin

Mine's a pretty simple heating only setup with a single LWT set at 45 degrees going via a plate heat exchanger, so quite a small primary loop.

Above 8 degrees outside, the unit cycles between on and off as requested "normally"

When the outside temp drops below 8, the unit drops the LWT to 35 degrees and keeps the unit on:



In terms of power usage, I've looked at the period between 22:00 on the 19th and 02:00 on the 20th.

Each 90 second burst of running uses about 30wh, which it fired 7 times in that 4 hour period. So it uses 210wh over those 4 hours.

I know some units get a 180w crankcase heater that run permanently, 24/7 all year


I'd love to know what setting they changed?

Did they turn the freeze prevention off?

Did they leave a new system config report?

Did they update the installer manual with the new settings (they should have)?






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  • 2 weeks later...

I don't believe that the engineer turned the freeze prevention off completely but I can't be certain as the weather has been quite mild.  He didn't leave a new system config report and he didn't update any existing documentation either. 

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  • 8 months later...

Hey all.  This is a work around to the Frost Proection Programme on the the Daikin Altherma Heat Pump which  causes undue noise in the middle of the night if used with a smart home system.  

Thanks to Octopus Energy for fitting this experimental solution for me, which works excellently

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  • 4 months later...

Just thought I'd post an update. After some to-ing and fro-ing the supplier agreed to swap out the ASHP for an Atherma 3. I have now had the replacement for nearly 12 months and I'm happy to say that the unit has worked flawlessly  and does not exhibit the "ice cube" problem of the previous unit. 

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