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Aerotherm and weather compensation

 
Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 28 minutes ago
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 DavidB
(@davidb)
Estimable Member Member
Joined: 9 months ago
Posts: 76
Topic starter 27/10/2026 7:43 am   [#3209]

Hi everyone.  I know this is not a new topic with lots written but finding a clear explanation related to our situation eludes me.  The AI tool certainly helps.  If anyone can refer me to a prior post, that would be appreciated.

Our 3.5 Vaillant Aerotherm is going well with the system permanently on and controlled with WC using a 0.4 heat curve.  We have 19C as our desired temperature using the thermostat in the wireless controller. During the afternoon and evening we use a wood burner to boost the temperature (we have a no cost wood supply) and as the wood generated heat dissipates overnight the HP takes over the heating.

In the morning, the temperature is normally about 18.5 and system is running.  What I don’t understand is the flow temperature is always below that which I expect from the heat curve - normally by about 2 degrees.  I recall something about hysteresis and Vaillant not wanting the temperature to overshoot.  My experience is it never seems to actually reach temperature unless there is solar gain or the stove goes on.  Can anyone explain what is happening?



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 5567
27/10/2026 8:22 am  

Posted by: @davidb
↑

.  We have 19C as our desired temperature using the thermostat in the wireless controller.

Posted by: @davidb
↑

 What I don’t understand is the flow temperature is always below that which I expect from the heat curve - normally by about 2 degrees.

These are likely inked. 

The basic explanation is that the heat curve, in addition to being adjusted according to the set slope, is also modified according to temperature set on the wireless thermostat.  This is explained in the manual for the sensocomfort (page 4 in this version)

If you think about it too deeply it initially takes a bit of getting your head around.  For most people, who wont compare FT to the curve, its not necessary to think about it at all!  Is is actually very sensible for several reasons which I can go into if you wish.  The easiest way I have found to rationalise it is that the slope setting (0.4 in your case) adjusts the curve to fit your house, whilst the set temperature on the sensocomfort adjusts the curve to your desired room temperature. 

The set temperature setting on the sensocomfort has some other effects depending on whether the 'room temp mod' parameter is set to inactive, active or expanded.  One of these could also be in play. If your 'room temp mod' is set to active and the setting of 0.4 is, in fact, slightly too high for your house the autoadapt function will kick in and tweak the FT down.

Hope that helps, feel free to ask more questions, you have a good piece of kit with lots of functionality, but of course functionality and complexity go hand in hand.

 


This post was modified 25 minutes 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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