DHW cycle interpretation please

Just getting into using & understanding our new Ecodan 11.2kW ASHP. In this image the heat output seems to disappear halfway through the hot water cycle with electrical input continuing. Made me wonder if my immersion heater is coming on but there’s never been the ‘lightening bolt’ symbol showing on the control panel which I believe indicates the immersion being on.

Is there a way of checking whether the Ecodan is calling for the immersion and if so keeping it turned off?


Looks like a problem with the flow meter, possibly trapped air, as the flow temperature continues to increase. Not immersion. Heat pump is fine, problem is with the measuring.

Just need to keep running the system and bleeding the radiators and auto air vents.

Related: Kamstrup Multical 403 Stops Working During Hot Water Cycle (Interference?)
And: Kamstrup Multical 403 Erratic flow readings


Exactly that.

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Thanks - that’s good news. Will check for air as you suggest

Thanks for the advice. Problem seems to be persisting. Can’t understand why it happens only with the hot water cycle? Am I right in thinking it’ll be fasely dragging down my average measured COP? Hot water cycle this morning had COP of only 0.85!

Anything else I could try?

It happens because unlike radiators there is nowhere for the air to hide (top of rads) and because it is hotter (more air dissolves out of water the hotter you get it).

What can you try?

  1. Remove the air

The system needs to be bled properly. Heat the tank HOT, then heat the radiators HOT, then flush all the air into the radiators by alternating between heating and hot water (heat pump off, pump on, cycle the diveter), and bleed the air from the radiators.

  1. Design it more robust to air

Mounting the flowrate sensor on the supply side (not return) after the system pump and increasing the static fill pressure (2 bar, if your system can take that) will both reduce cavitation within the heat meter’s flowrate sensor.

  1. Sanity check there are no mistakes

You also need to check the position of the flowrate sensor isn’t somewhere that it will be adversely affected by air. The meter installation manual will show where it should and should not be fitted.

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