Kamstrup Multical 403 Erratic flow readings

I’m running the Kamstrup Multical 403 on my setup 7kW aroTHERM+ (Rushden, Northamptonshire on Heat Monitoring Dashboard), installed early July 2023. I too have issues with DHW reporting which we are looking into. It shows the same erratic recording of flow temperatures. Photo of setup:


Flow temps or Flow rates John?

It might worth starting your own thread John? Post up some screenshots from your openenergymon during DHW runs?

And if you view the vaillant controller during the runs, what does the flow rate show? is that constant? or does it drop/fluctuate?

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Thanks Mick, my post was really to left @ajdunlop know that he was not alone with issues with the setup.

Mark my heating engineer is planning to visit to move the heat meter location. I will create a new thread once that has been done with before and after readings.

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Sounds good.

I think it would be good to see what you’re seeing now though and how things change over time.
Having a quick look, yours looks like different symptoms to Andrew.
His is wild flow rates, whereas yours just drops off to zero?

What makes you/Mark think moving the meter will resolve?

Damon moved mine 3 times to little / no effect. See link to Sharky thread earlier in this thread.


Hopefully we can all contribute and help you get this sorted. :+1:

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Thanks for flagging this @johntony

@glyn.hudson and I interested to hear if you can resolve this as well!

Can you hear any air in the system? what’s the system pressure? looks like it’s in a loft/roof is that the highest point?

@glyn.hudson’s just added reading of the error registers on the kamstrup so that we can monitor those. I think it might just require an emonhub update to make them appear in the emoncms inputs.

Glyn’s also shared this with me, which might be useful:
The challenge of correct flow sensor installation with respect to flow disturbances.pdf (517.7 KB)

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I can see this example from your dashboard, looks like similar temperatures to the area where the heat readings drop out at 10:20 are later reached by the space heating period but it’s much cleaner. I found with my system it took a while to get rid of all the air in the hot water cylinder coil, due to the high surface area corrugated coil…

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I think there are some similarities. There appears to be changes between 1min averaged valves (steps) and smother more frequent values.
Also I have been trying my pump on a higher setting and getting the power drop to zero later in the run.

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I can’t hear any air in the system. Pressure is 1.9 bar. Yes unfortunately it is at the highest point, there’s nowhere else lower elevation of pipework, apart from outside. Thanks for the PDF will read.
Thanks for the new thread too. :smiley:

Pressure and no audible noise sound fine, have you listened out for it just as it switches over to hot water?

I’ve added some more details which I hope gives some additional background. Mark, my installer and I noticed that we were seeing cycling on emoncms view and thought it was the buffer that was causing the issues. The buffer and Yonos pump was removed beginning of August. Since then I’ve been keeping a daily log of our DHW heating cycles (attached PDF). I’ve been changing the charging offset and hysteresis settings thinking it was the heat pump causing the cycling.

Glyn unprompted by me emailed me and he things:

“…your HP is working fine, it’s not cycling at all during a DHW cycle, notice the electricity consumption and flow temperature is a nice smooth trace. The spikes you can see in the heat output is the heat meter incorrectly reading the flow temperature.”

This belief is supported by the Valliant controller showing a working figure for the month of August at COP 3.4 for DHW.

DHW settings and performance Aug 2023.pdf (1.2 MB)

Seems I was barking up the wrong tree with tweaking the heat pump setting. It appears to the erroneous flow temperature readings from the heat meter might be the cause. This was why Mark and I thought moving its location away from any bends / valves or tweaking the existing layout to remove the double bend just after the heat meter. Flow is from right to left as you look at the photo. Note: needs a tidy up and re-lagging after removal of the buffer tank.

This was the most recent DHW run on 15th August.

Oh this sounds like it could be useful. Is the error register viewable on the heat meter just for instantaneous errors or do the persist for a while? If they are the former then being able to log them out would be good to see if there are any clues.


No, but I will do that. There’s the standard Honeywell 3 way valve installed.

Im not sure, @glyn.hudson will know or he may just have enabled reading the registers with the intention of helping with the issues you are seeing.

I’ve updated EmonHub on my emonHP to master so now logging on time and error time hours. Will have a look to see if the error time increases tonight.

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I have the same setup and see exactly the same fault

This is when I heat water for a longer time. If I just run for a short time then all appears normal

When I look at the meter display it is showing error when the heat measured dropped out. This error code is for air but only seems to happen on longer runs for DHW. Cylinder is a Mixergy with plate heat exchanger.



Thank you for this information Dave. I will try a short run of hot water today and report back. Not a fix, but interesting to see if my use pattern matches yours.

anti legionella run last night. The problem seems to occur once the pump starts to ramp down as Flow temp has hit water heating temp

What’s the flow rate showing when it starts playing up? Can you add that to the graph?

Update from me. This afternoon I cleared out our magnetic filter (nothing on the magnet but was a bit of black before it ran clear). Then manually operated the pump for a while alternating the 3 port valve to try and get rid of any air by my trapping it in the rads.

I then did another hot water heat up shown below (ignore the bit at the start that was me toggling the 3 port valve):

This was on the top pump speed and as you can see the power output and flow speed readings drop to zero part way through. The temperature values go from 1min to 10 sec and back to 1min again.
Also the OnTime_Hours_error increased by 1 at 18:21

Yes it looks to be around this point that the strange things start to happen. The problem seems to be worse for me the higher the pump setting but the point that it all goes wrong isn’t triggered by flow rate as this isn’t being controlled by the heat pump so should remain fairly constant on DHW.
The only thing I can think of is some change to the behaviour of the flow through the meter once around that temperature is met or the creation of more air bubbles at that temp.