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Daikin DHW Margin - what is it?

 
Air Source Heat Pumps (ASHPs)
Last Post by Toodles 6 months ago
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 Pipcart
(@pipcart)
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Topic starter 12/01/2026 4:45 pm   [#2737]

Our Daikin Altherma 3 Monoblock has DHW settings for both Hystersis and Margin. As I understand it, the hysteresis is the difference in temp between the target temp and the temp to which the tank will drop before the tank is heated again, back up to target. Daikin also have a Margin setting and the descrption of the margin that today's engineer found seemed to mean the same thing as the hysteresis - he didn't know the difference between margin and hysteresis either. However, I know from another engineer that there is a difference, it's just that I can't remember what he said!

Does anyone know how hysteresis and margin work together for Daikin DHW, please?



   
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Toodles
 Toodles
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12/01/2026 5:35 pm  
  • I don’t use our Daikin for DHW so can only make a guess at this. Your are right about hysteresis though; I suspect that margin may be related to ‘tolerance’ in as much that if you have a TOU tariff to take advantage of, the water may be taken to a higher temperature during the ‘cheap’ tariff times. This marging may be perhaps a further 5 degrees or so enabling you to obtain a greater capacity when diluted for use. That is only a guess and I expect someone with far more knowledge than I will be along to give us the lowdown. Regards, Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.


   
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 Pipcart
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Topic starter 12/01/2026 5:38 pm  

@toodles Thanks!



   
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Toodles
 Toodles
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12/01/2026 6:44 pm  

@pipcart A further search rather suggests that someone at Daikin needs to re-write at least one section of the instruction manual; I reproduce some further confusion below:

“The

"margin" setting on a Daikin Domestic Hot Water (DHW) system, often referred to as hysteresis, determines how far the water temperature is allowed to drop below the target set point before the system automatically activates the reheat function. 
This setting is designed to:
  • Maintain a consistent background temperature: The system will only initiate a heat cycle (using the heat pump and/or the electric booster heater) once the water temperature falls by the value set in the margin.
  • Optimize efficiency and running costs: A larger margin means fewer, longer heating cycles, which can be more efficient than many short bursts of heating. Users on specific electricity tariffs (like off-peak rates) often set a large margin to ensure heating occurs only during cheap rate times.
  • Prevent excessive cycling: It stops the heat pump from continuously turning on and off to maintain the exact temperature, which reduces wear and tear on the system's components. 
For example, if the DHW reheat set point is 45°C and the margin (hysteresis) is set to 5°C, the system will only start heating the water when the temperature in the tank drops to 40°C. 
The specific menu number for this setting can vary depending on the model (e.g., it might be 6-01 on some models), and installers or users can adjust it via the Daikin MMI (man-machine interface) to suit their hot water usage patterns and electricity tariffs.“About as clear as mud really - very sorry!😟 Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.


   
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 Pipcart
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Topic starter 12/01/2026 6:51 pm  

@toodles Well that cheers me up really - I can understand why I'm confused! I've decided to reduce the margin to zero and see what happens with just a hyteresis setting. Looks as though they may have a duplicate setting (?). Many thanks.



   
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Toodles
 Toodles
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12/01/2026 6:54 pm  

@pipcart Please report back in due course - this may be very enlightening indeed! Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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 Pipcart
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Topic starter 12/01/2026 6:55 pm  

will do



   
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 Pipcart
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Topic starter 23/01/2026 12:19 am  

@toodles Having reduced the margin to zero and kept the hysteresis at 6 the tank now varies between 44 and 50, as expected. I'm not usure, but I think the margin of 3 sometimes allowed the tank to go below 44, but I can't be sure. Anyway, the upshot is I will keep the margin setting out of the equation - can't see the purpose of it 🙂



   
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Toodles
 Toodles
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23/01/2026 11:38 am  

@pipcart Can’t help wondering if it has come about through some lazy ‘cut and pasting’ when compiling the code for the controller and using some existing programme as a template so to speak. Regards, Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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