Ämne: drop of supply temperate - Nibe f2040-8

[ja100]

Hello, im hoping someone could me with this.
och förlåt för Engelska, jag försöker fortfarande lära mig !

So I have the Nibe vvm225 and f2040-8, underfloor heating downstairs, upstairs rads.
Its gotten colder in Stockholm the past few weeks and I am seeing some strange occurrences with regard to the supply temp I am getting (and thus indoor temperature)

on the 25th November, as I recall it was pretty cold in Stockholm, around -5/-6 and was consistently getting supply temps of 44-46

on the 26th, I think it was a little warmer even, but for some reason supply temps could not get above 36-39. I didnt change anything on the boiler, heating curve was the same etc. The big surge around 1am is getting hot water.

Anyway it has happened again today, no idea why, but was getting around 42 this morning, and dropped to 36-39 again and consistently getting that today. Again, nothing has changed on the boiler so cannot work out why this is happening. It is easily able to get warmer temperatures, as it is getting close to 60 when filling up hot water. Any ideas? thanks!

[ja100]

it has dropped considerably now and had to put the addition on now which is not ideal!
only thing I can think is the snow, there is heavy snow in Stockholm at the moment, well around 6 inches and it has been snowing since around 3 hours now, which seems to be inline with the drop in temp. Is it that the snow hitting thing at the back that gets icy (evaporator?) means it cannot get as much supply temp?
I cleared the snow around the heatpump the night before last, so it is not covered in snow or anything, but is it that if there is snow *around* it means it cannot get the supply temp?
thanks to anyone that can respond !

[Carl N]

Can you check menu 4.9.2?
There is a value "Start immersion heater" or somthing like this (I don't have the english manual).
Outdoor temperature above this will block the immersion heater, try to increase this value and see if make any difference?

[ja100]

If I put this higher it means the immersion will come on right? I had to do that earlier - what I meant by ‘turned on the addition’ but I want to avoid this as it much more expensive. And the screenshots I have attached do not have immersion on- only the heatpump.

[Carl N]

Well, the only explanation I have is that outdoor unit is frosted and the defrost function don't work optimally?
Can you plot the BT16 in the same time?

[ja100]

That’s from 25th ( good supply temp), 26th ( bad supply temp) and today (bad supply temp) but can’t see what’s good or bad ?

[Carl N]

 
It is a bit tighter between the defrosting cycles in the end of 25th when supply temp drops.
And the BT16 value goes down to a lower temp before defrost both in the end of 25th and whole day 26th and 30th.
The temp sensor is probably OK as it shows almost the same temp between cykles, but it drops faster and to a lower value... 

Is the fan working as it should?
Maybe it don't speed up when lower outdoor temp as it should?
Also check 5.11.1.1 that silend mode is not enabled?