Kamstrup Multical 403 Erratic flow readings

We don’t do any filtering, we just read the meters every 10s and report the raw data.

With regard to filtering, I have noticed the Kamstrup will report power in 100W increments, while Sontex will report power in 1W increments, not really a big deal when heating power is usually 1000W+

Yes, this should be possible. We don’t lock the meters.

yeah, air:air a lot more common, split type, not centralized hvac systems, not on residential anyway.

looks like the unit is a bit over powered for my needs so when trying cooling i get some awful short cycling. i got it to behave better by adding the missing after buffer temp sensors. it fares better on heating, but will monitor closely, season just starting. will leave it in and add some bypass pipe with ball valves so i can try one or the other. the buffer i think is a mixing tank of sorts, all inlets and outles lead to the same tank, no serpentine. was thinking of leaving it in the circuit as a “volumizer”

good luck with your setup.


It is the heat meter that will be doing the filtering.

If the integration period (measurement interval) on the meter is only 32 or 64 seconds (which it may be on a Kamstrup, depending on what you order / how you configure it) then the meter can EITHER report “last” reading or some “filtered” reading.

Take a look at the display on one. Start with zero flow. Whack the pump on. Watch to see if the display jumps straight to full flow or does through a period of increasing flow even though you know full well that the flow jumped up imediately.

Take a look at the M-Bus output. Those slides I shared were comparing a Zenner C5 with a high resolution turbine meter and you can clearly see the output of teh C5 is taking time to rise and time to fall because therere’s amoving-average filter on the output.

These non-fiscal registers are non-regulated; so behaviour varies between makes / models/ configurations.

Small Kamstrup meters usually state power rounded DOWN to the nearest 100W. If you are using the “cumulative energy” figure then this doesn’t matter. (there is no rounding) If you are using “instantaneous values” and then integrating at server level to work out energy then it is more accurate to use the flowrate (provided to the nearest litre per hour) and the temperature difference (provided to the nearest 0.01K) than it is to use power rounded down to the nearest 100W.

You can get a feel for the magnitude of any error by checking how well “estimated cumulative energy” matches “fiscal cumulative energy” - say from 01/01/22 through 31/12/22 what was the chance in the cumulative energy register vs the energy delivered if you multiple instantaneous power by time betwen samples and sum that?

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@Dan_Nichols ordered from Stockshed rather than OEM though so it’s anybody’s guess how that unit ships!

403 manual, page 21, has the same setup loop coding as the 60 manual fww:

If you can satisfy the minimum flow requirements of the heat pump with it setup as a volumizer that will behave better. :slight_smile:

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Adrian at Stockshed confirmed that the 403 is shipped configured for installation on the return, so I’m good there. He said as @markocoheat mentioned that it can be reconfigured before water runs through it for the first time.

@markocoheat any other setup changes you’d suggest before putting water through it?

As I’m not worried about sealing it (no billing requirement) am I able to access setup again by breaking the seal as mentioned in the manual on page 21?

For a heat pump no. Integration times are not important.

Yes you can break the seal up to 50 times. Some settings will still be available. Others only with software and optical eye. After 50 breaks it lock locks; and on the 403 unlike the 603 you can’t just change the head you have to change the whole thing.

The 603 BTW isn’t as good at error codes for air etc because it uses pulses between the flow sensor and the head rather than being direct connect. So you can’t as easily see if there is air happening at certain times / during certain events.

how far away from the plate exchanger can the temperature sensors be? would 1m of pipe be ok if i add thick insulation to it?

Doesn’t matter.

One temperature sensor should be next to the flowrate sensor. The other tempeature sensor can be anywhere. You’ll be measuring the heat crossing “that boundary line” though; so any heat lost from the plate/pipework up to where the heat meter is measuring temperatures won’t be measured.

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An update on my bad DHW measurements.

It appears that now heating has been running properly for a bit that my heat output measurements are improving.

The flow rate only fluctuates a bit if the DHW cycle is preceded by the heating being on:

However the flow still drops to zero if the heating wasn’t on before:

There is still some air collecting in a couple of rads after a while.

Thankfully my over all COP figure is improving on the heat pump monitoring dashboard now that most of the output on hot water is being captured.


Looks like you’re slowly eliminating the air from the system @ajdunlop - if you’ve flushed it into rads before the DHW cycle (hotter water can hold less air; air collects in the rads as a bubble of free air) then the DHW cycle runs largely untroubled; but if it’s had time to cool; the air dissolved back into the water; and that water with dissolved air in has made it back to the heat pump / tank then when you run the DHW cycle out comes the dissolved air as the water reheats.

My Kamstrup 403 was suffering with air during hot water cycles shortly after install on the 9th Nov.

Within a week (15th Nov) the air looks to have cleared and readings are more reliable.


thank you veryone for the help, i now also have my kamstrup 403 installed and started pulling data.

not sure if this was the proper thing, but the data I was getting was not complete, was missing flow for instance. I opened this, changed data pulled for kamstrup403 by tzapu · Pull Request #204 · openenergymonitor/emonhub · GitHub but maybe i missed some other way of doing it. thinking of it, should of made a new post about kamstrup 403 …


Hi Marko,
could you please share prog531 with me (for personal use only! Promise no reshare of any kind!)
kuockep at gmail com
Thank you very much in advance!

Sent @skoff

having a few issues on a newly installed heatpump with this


It can take a few weeks for the air to work it’s way out of the system so I wouldn’t be concerned unless the system has been running for a month or so since it was last filled.