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Nibe F2040 periodic warm water increase fails

 
Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 3 hours ago
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 tribol
(@tribol)
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Joined: 5 hours ago
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Topic starter 20/05/2025 8:59 pm  

Hi all,

I recently bought a house and am now a proud owner of a Nibe F2040 Heatpump with SMO20 controller. I observed that after each periodic warm water increase a warning appears on the controller, stating that the desired temperature cannot be reached. The maximum temperature which is reached after ~30 min is 54 °C (independently of setting the desired temperature to default 55 °C or 60 °C). When someone inspecting the heating installation came to the house in February, he speculated that the temperature could not be reached due to too cold temperatures. However, since then the warning is still occurring on every try of a periodic heating increase (2 weeks).

I logged temperatures on the SMO20 via USB while doing another unsuccessful hot periodic increase for finding out more and would like to ask for your experienced view on what might be wrong:

I observe that once the periodic increase is initiated at ~18:53, the pump starts running at 70 % and the heatpump starts working with a visible increase in BT3 & BT12. Similarly, the water temperature is also increasing. At 18:57 the pump speed drops to ~30 %. At 19:32 there is a sudden stop in BT12 increase, correlating with triggering of the alarm 162. The alarm indicates that "Condensor out has reached max permitted temperature" and does an automatic reset of the heatpump. From there on it's understandable that the warm water temperature is not increasing anymore, not reaching the target of 55/60 °C.

I have plenty of questions and am grateful for any ideas and opinions:
- How can I solve this issue or is this an issue at all?
- Would increasing the pump speed help in flattening the increase in BT12 such that the limit of 60 °C is reached later, allowing the warm water to heat up to the desired temperature?
- why is the pump speed suddenly dropping?
- If the alarm limit is at 60 °C, then it will never be possible to reach a periodic hot water temperature of 65 °C, which is also an option that can be set on the controller. I think I'm missing something here. Could it be that high temperatures can only be reached with the additional heater?
- regarding the additional heater: as the outside temperatures are ~ 20 °C, the additional heater is not active. Should it be active? Is there a way to activate it only for the periodic hot water increase?

Thanks a lot for all your help!

failed periodic increase
This topic was modified 4 hours ago by Mars

   
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 JamesPa
(@jamespa)
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Joined: 2 years ago
Posts: 2457
20/05/2025 10:49 pm  

Many people with heat pumps heat water only to say 48 with a weekly legionella cycle (often using the immersion) taking it to 60/65.  This should all be set up on the controller (look for a setting for legionella or disinfection). Heating to 60 every day significantly decrease efficiency and in most cases adds no utility.  You only need about 40C at the tap, any more feels too hot.

Depending on your dhw cylinder and spec of the heat pump 55 or 60 may well be unachievable.  It's certainly not desirable in most cases so unless there is a good reason to do otherwise I would eliminate the error and save yourself some money by reducing the set temperature to 48. 

I could go into more detail but if the obvious answer is ok that's in short the best way forward.

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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