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Buffer Tank Dixell Setpoint vs Weather Compensation Flow Temp on Altherma 3M Heat Pump... Will It Ever Trigger?

 
Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls
Last Post by Lbart68 4 months ago
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 Lbart68
(@lbart68)
New Member Member
Joined: 4 months ago
Posts: 2
Topic starter 15/05/2026 12:59 pm   [#3000]

Hello, I am completely new to heat pumps having moved into a house with one I wasn't involved in the install etc so trying to understand it all.

I'm trying to understand around the buffer tank and the set point on the dixel controller. What should the set point be set to as I understand that it only triggers the circulation pump when it reaches that +2c but if the WD curve is currently 25C and the set point is 30c, it won't ever reach it I thought? Sorry if this is dumb question 


This topic was modified 4 months ago by Mars

   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5399
15/05/2026 3:47 pm  

Hi

Welcome to the forums and please be assured that no question is dumb. 

Just like boiler based systems, heat pump based ones differ from house to house.  If you can tell us more about your system, the key components and controls, I'm sure we can work it out.  If you have a system diagram then please post it.


This post was modified 4 months ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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 Lbart68
(@lbart68)
New Member Member
Joined: 4 months ago
Posts: 2
Topic starter 15/05/2026 4:00 pm  

Hi,

Thank you.

 

So its a Daikin Altherma 3M in a new build that has 2 zones with hive thermostats. I've attached a couple of photos of the controls/cylinder. No system diagram and nothing left for us beyond the manual.

I've got my head around the WD curve but its trying to understand how what I've established is a Dixell controller on the cylinder

PXL 20260515 145530485
PXL 20260515 145351173

works with it... From what I understand, the current buffer tank temperature is 26c and its set point is 30c. It needs to be +2c from the set point to trigger the circulation pump but in my simple brain, if my WD curve is set to 25c for current temps, then the pump won't ever activate but then obviously flow temps change but the set point doesn't so I don't know what to set it to or what I should do with it



   
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