Help with Nibe F2040 12kW SMO20 system

Charge pump hot water was set to auto:

I have set it to manual as Dave suggested and have set the speed at 75%

BT25 sensor is located just below the red valve

OK, good. Let’s see what happens on the next DHW cycle.

In ‘Auto’ mode, the control algorithm chooses the Charge Pump speed to (try to) deliver the requested delta-T. For some reason, that algorithm has been coming up with a too-low pump speed. Forcing it to 75% will let us check what happens when the DHW coil is getting a more reasonable flow-rate.

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Thanks @dMb - I attach some screenshots of how it’s going. (I’ve set DHW to off during the peak Agile period of 16:00 - 19:30).


Latest data following changes.


From this morning.

Thanks for the new graphs. So that’s looking a bit better, I think?

Would you be able to post a graph rather more zoomed-in around the 08:00 DHW cycle please:

  • You can omit GP1 (pump speed) since that’s clearly taken effect at 75% for DHW
  • Please include BT12 (Flow temp)
    • I’m curious as to what the delta-T looks like (BT12 - BT3) and how BT3 compares with BT6

I was going to say you could omit BT25 (since that’s just for the CH circuit) but it looks like BT25 is increasing during the DHW cycle, which is “interesting” (i.e. unexpected) so please retain BT25 in the zoomed-in graph.

@etchelsa was it you who had issues with the diverter valve not fully switching over? If that valve is still sending some water to the CH circuit during a DHW cycle that might explain why the DHW cylinder is struggling to heat up…

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Hi @dMb - thanks again for having a look. Chart attached - another DHW run just now as well as around 8:00 this morning. Comfort mode is set to Economy (all default temp settings as far as I know).

I wonder whether the immersion in the DHW tank is running as there seem to be peaks in our electricity load coinciding with DHW runs.

You suggested @dMb previously potentially switching the immersion to “off” on the wall mounted switch box - I wonder if it’s time to have a look at how that would affect the system?

Sam gets the credit for that suggestion - but yes, I think it’s worthwhile, to eliminate the variable of the immersion heater kicking in.

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Yes! Thanks @etchelsa Sam :smiling_face:

I’ll switch it off now - I’m going to run a “Normal” DHW session this afternoon while Agile is relatively cheap.

Here are my thoughts on the 12:00 DHW cycle - now we know the Charge Pump is running at 75%:

It will be interesting to see what happens with the Immersion switched off, to gauge how much of the BT6 increase is coming from the heat pump.

(My system doesn’t have the immersion switch; there’s some sort of built-in heating element within the Ground Source unit’s enclosure and the immersion in the DHW cylinder is completely separate from the heat pump (actually connected to an ‘immerSUN’ solar PV diversion unit)).

It does look like a slightly better delta T on flow and return now.

Yes it is my system that’s got some problems with CH and DHW isolation. I haven’t yet worked it out but something in my CH flow cools my DHW which suggests I have some links between the DHW plumbing and CH plumbing. I know my red valve is plumbed backwards but wired correctly. I need to take it off, orientate it properly and try again. I’m waiting for when I don’t have reliance on heating just in case. I always have the immersion to bail me out for DHW but no back up heat source for CH.

I’ve noticed the same behaviour on Katherine’s plots as mine. The DHW temp drops during CH cycles and eventually the HP gives the DHW a quick boost at the end of a CH cycle. It’s shown by a saw tooth effect on the BT6 graphs. I have been able to determine this saw tooth loss on BT6 is caused by something other than natural losses from the DHW cylinder because when I turn the CH off the BT6 loss stops and the temperature holds steady all day.

It might be worth looking at how the red valve is orientated. Can you take a picture of the brass valve body (it should have A, B and AB engraved on it) and also the top of the red valve case (it should have A,B and AB shown in white writing). We can check if all this is orientated correctly.

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Thanks Sam @etchelsa - I took these photos yesterday as I had a hunch this might be something to do with it.

I’ve noticed that ever since the system was installed we get a spike coming through the CH when the DHW cycle runs. This is very noticeable as we can hear the kickspace heaters in the kitchen coming on, and this happens even in the summer when there is no heating demand at all.

This looks correct. Default is CH (AB->B flow). This aligns on the fitting and the balance body. When the SMO controller wants DHW it energises the black wire and the flow goes AB->A.

You may have a problem with the valve itself (as might I) but I haven’t been brave enough to take mine off yet and test it on a bench.

The behaviour you have observe with the heaters does seem odd. What cause these to come on? I’m not familiar with this type of emitter