I send a greeting to this community. I would like to present a situation that I have not yet been able to resolve, although I have had discussions with 2 Nibe representatives in the area. I do not know if I can post graphs at this time, being a newcomer.
I can briefly describe the situation: Nibe F20240 10-16 pump, split, panel radiator heating, usable heating area 160 sq m, 2 levels. The pump works in parallel (if necessary) with a gas central heating system. Since the beginning of January, the pump has only been operating with a BT25-Bt71 difference is max. 3 degrees. Also, the Supply line set point is constantly 45.0 °C. DM constantly between -700 and -850. BT50 has no influence. Regardless of the outside temperature, the temperature in the house is approximately 24 degrees, the target being 21.5.
No setting made affects the behavior of the Pump. The installer even did a Factory reset.
When I have the opportunity, I will also post graphs. Hoping that I have captured some attention, I thank you in advance and await reactions.
Welcome to the forums and thanks for your post. That does indeed seem very strange behaviour - almost as if there is a hardware fault of some sort. Presumably there are no ‘Alarm’ conditions being raised though?
If the Degree Minute value is never rising above -700 the controller will always think it needs to deliver more heat, which probably explains the constant 45C set point.
What sort of readings are you getting from sensor BT25 and how do those relate to the S1 target?
There is a tick-box in one of the configuration screens which specifies whether BT50 is used to control the Heating or not; is that ticked ‘On’?
Thanks Vali. That’s the setting I was referring to, so BT50 at 24.2C (with an Indoor Temperature Set Point of 21.5C) should be tending to reduce the S1 Calculated Target flow temperature - to some extent. With the SMO S40 I don’t believe there’s any way to control how much S1 gets influenced by BT50 (with the older NIBE controllers there’s a “factor” setting you can adjust).
Which WC Curve is it running on, and what does that specify for the Calculated Target flow temperature at your current BT1 Outdoor Temperature?
Hi David, I can say that the technician from the Nibe representative had access to the system and made various settings and monitored various climate curves. Now the system works on climate curve 4 with offset 0 (I know, it seems small for heating with radiators). I tested a period and a curve of my own. The problem is that no setting changed the behavior of the pump. To use a figure of speech, it is like a car that drives at approx. the same speed no matter how much you accelerate it, brake it, no matter how many curves, slopes, ice on the road… It runs on a locked autopilot). In fact, it is as if the climate curve does not work.
Thanks Vali. That is indeed really odd. The WC Curve is saying the Flow temperature should be 35C at 0C Outdoor temperature - and the too-high Indoor temperature (from BT50) should be reducing that Calculated Target flow temperature - but the Calculated Target is always much higher, at 45C?
I’m afraid I’m just confirming what you already know - that this is Not Right and doesn’t make sense (at least not from how I understand NIBE controllers to work).
It’s possible that with such a highly-negative DM value the controller is applying some special logic to try to recover the situation, but you’d hope that the NIBE specialists you already have involved would be aware of that.
Thanks David. Just kidding, it seems like the pump has “lost its mind” but the Nibe ‘psychiatrists’ can’t make a diagnosis. Unfortunately, the Nibe technicians are overwhelmed. Too bad that a brand considered premium is so “poor” on the troubleshooting side.
Just to confirm, is there nothing at all in: System Profile > Event Log?
No ‘Alarm’ or ‘Warning’ messages?
All I can suggest is further simplifying the configuration in the hope that gives a clue as to what might be going wrong. For example, un-tick the setting for BT50 to Control the Heating (which seems to be having no effect anyway), so the controller purely runs on Weather Compensation.
If there’s some way to re-set the DM counter to 0 that might help too - in case it’s attempting some sort of emergency heating with such a highly-negative value. I think a power-cycle should reset the DMs to 0.
Hi David. Thank you for your helpful questions. Chronologically, on 15 Jan I received an error message: “Freeze protection
01/15/2026 • 07:16
Temporary forced control of room heating is activated to prevent damage due to freezing in the home. This is due to low outdoor temperature combined with room heating being blocked. Freeze protection deactivates automatically if the outdoor temperature increases or room heating is activated.” I immediately tried to contact the Nibe representative. It took a few hours for him to answer the phone - all the while I was receiving error messages. The Nibe representative took control via the MyUplink app and made various settings. At one point he guided me to a reset of the pump fuses - wait 15 min, then restart. This was done to give the capacitors time to discharge. The error regarding Freeze protection disappeared. I have performed the DM reset and BT50 deactivation for a few days under the observation of the Nibe representative, the pump behavior remained identical. I was thinking of trying to switch the pump to a manual mode but I am not familiar with that menu or what it involves. Do you have any suggestions regarding this attempt?
it does seem odd but I can’t quite piece together the story (might just be me).
putting aside the effect of BT50 for a moment, with that weather curve I would expect your target temperature (S1) to remain exactly the same at any outdoor temperature - at this time of year, This should be 35 degrees. Are you able to post a graph of S1, it’s hard to tell from the graph what the value actually is. Do you have any heating schedules set? These influence S1 too so we should clear those if so.
It might be helpful to log and graph your data similar to what we have supported other Nibe users with. Then we can really see what your S1, flow and return temperatures and degree minutes are doing.
Obviously Nibe are looking but it doesn’t seem to be getting you anything overly helpful.
Hi Sam, I’m glad you joined this debate. Regarding the aspects you raised, I can say that S1 (Calculated supply climate system 1) was and is 45 degrees, without any deviation regardless of the outside temp. I haven’t set any heating program. Starting with February I started recording data every approx. 24 hours. I’m now posting a first graph that I hope can be read more easily.
Ieri seara am facut unele modificari care se observa in grafic. Am redus debitul la pumpa de circulatie externa (Ferroli LAP25-6-180) de la treapta III la II apoi la I. Primul efect, DeltaT a ajuns la aprox. 6 dupa 2 luni de max. 3. Am taiat influenta BT50, am setat influenta WC la 4, iar curba la 4 cu offset -4 ! Am resetat DM dar din pacate a revenit la valori de -700
so if BT50 is out the equation (you said it was unchecked) I am now wondering what your outdoor temperature sensor might be thinking. I can’t see anywhere in this thread where you mention BT28. I believe the BT28 temperature reading is what the controller uses to select a S1 target temperature (by looking up the value from the chosen curve). Based on your curve the BT28 reading would need to be about -40 to give S1 at 45 degrees. I can’t believe this to be the case but it would be good to rule out a problem with BT28.
also are you grabbing this data from Nibe uplink? Can you add BT28 to a graph?
