Kamstrup Multical 403 Erratic flow readings only during DHW heating okay heating radiators

Hi,

Mitbushi Zubadan PUD-SHWM100VAA with Level 3 Heat Pump Monitoring, Kamstrup Multical 403.

Flowrate during radiator heating is constant at 22l/m but during DHW heating flowrate is very erratic, dropping to 0.
Here are both radiator heating cycle and DHW heating cycle showing flowrate.

Here is DHW showing okay flow rate 22l/m okay, up to a temperature of approx 43 deg flow temp and 40 deg flow return, but flowrate drops to 0 with few spikes to 14l/m even though DHW heating continues up to 53 deg flow /50 deg return.

Because flowrate is not right then COP is not correct for DHW.

Flowmeter is on return pipe as below.

Pressure is approx 1.4bar, I have just increased this to 1.6bar and will see if it improves.
There is air vent at high point where the flow pipe enters the hot water tank.

Any help would be appreciated.

I had exactly the same with my system which was down to air in the system. I sorted mine by running the radiator heating hot and bleeding the radiators a lot. After a couple of days the DWH cycle starting working correctly

2 Likes

As Dave says, you’ve got air trapped in the hot water circuit, which messes with the flow meter. Kamstrup’s are particularly suceptible. Should be fine once the air is removed.

It sounds like you have some air in the system. Also, the location of your meter on the piecework is not recommended. It looks like your meter is in position F on the inlet to a pump:

The Kamstrup install diagram above states that a meter “must never be placed on the inlet side of a pump”

Hi,

The meter is located on the return on the outlet side of the pump.


Blue arrows shows return direction,bottom to top, pump followed by meter, followed by filter.
Flow is shown by red arrow down to 3 port valve, yellow arrow right to DHW cylinder, or orange arrow down and back thowards wall and to all radiators.

I did a heating cycle with high temperature followed by bleeding radiators and then a DHW cycle.
Improvement but still flowrate erratic for last half of DHW cycle.

Will try bleading radiators a few more times as people suggested.

Thanks for all suggestions

You will probably get there eventually.
I had the same issue. I installed mine during the summer and it didn’t really fully sort itself until the heating season which helped the air to make its way eventually to rads to be blead off.

Ah right, sorry I didn’t notice it was a split system. Usually for monoblock systems, the return would be heading downwards towards the outdoor unit.

Yup I’d agree with other comments that this looks like air in the system. Had the same issue with my own Kamstrup 403. It took me several days of topping up the system pressure and venting the air out to clear it all. You should hopefully get there after a while.

1 Like

On the plus side you’ll be doing the system a lot of good by getting all the air out. There will be less corrosion etc; longer life. :slight_smile:

That’s another win for OEM, for sure. Without this data we’d have [almost] no idea that there was still air trapped in the system. We might think to bleed the radiators once in a while [especially approaching/during heating season] but wouldn’t have an indication like this that the system was not fully vented.

Hi
Unfortunately I could not find any air in the system so far by following the suggestions.

As I have a split type heat pump, when heating the DHW there is only about 2 meters of pipe between the Ecodan Hydrobox, circulating pump and the cylinder but when doing heating of radiators there is a very long amount of pipework.
The same circulating pump (Tucson Type RS25/6EAQ130 6 meter head) is doing both the DHW and the radiator heating and the installer had set the pump to Speed III (Pump runs at a constant speed) and the flowrate was at 22l/m on both DHW and heating cycles.
I have tried switching the circulating pump to CP1 setting (Lowest constant pressure curve)
(The duty point of the pump will move out or in on the constant pressure curve, depending on the heating demand. The head (pressure) is kept constant, irrespective of the heating demand.)

With this I am now getting a constant flowrate of approx 13l/h with no erratic readings when doing DHW and 22l/m when doing radiator heating.

DHW cycle now looks like this

and heating cycle looks like this

Are there any negatives to running the circulating pump in Constant Pressure Control mode instead of fixed speed ?

There will be a larger temperature difference between supply and return temperatures, for any given power output, if the flow rate is reduced.

The elevated supply temperature (for a given average temperature) will reduce COP.

There will also be a reduced pump power.

This will increase COP.

The optimum balance between these two (the optimum temperature difference for a given set of operating conditions) will vary by heat pump and by operating condition.

If anything, the behaviour of this ecodan appears more stable (the supply temperature is wobbling about less) with the 5 degC difference now compared with the 3degC difference before…

Search the forum for ecodan and john cantor and you will see other evidence of the ecodan control systems struggling to operate in a stable/efficient way with lower temperature differences.

The unit is probably happier now than before.

The air in the system will be dissolved air that is only coming out of solution in the lower pressure (Venturi effect) flow rate measurement part of the heat meter. This venturi effect is reduced at lower flow rates which is probably why it is now not tripping error codes.

1 Like