Dip during DHW cycle

Would appreciate any insights you may offer on the dip in flow rate and heat, please?

Asking with respect of my heat pump, not what’s monitored/rendered on emoncms.org

The reason for the gap in blue shading for DHW is because I created a template helper in Home Assistant that bases the DHW state on three properties. Space heating circuit being “STANDBY”, flow temperature > 20C and flow rate > 0.3

I initially just used “STANDBY” as the toggle but when I tested enabling ECO mode for space heating when in setback, the Vaillant API returns that value not just when it’s doing DHW.

Looks like a problem with the flow meter, possibly trapped air, as the flow temperature continues to increase. Heat pump is fine, problem is with the measuring.

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

I’d agree with @Timbones that erratic flow is symptomatic of trapped air in the hot water pipework. It took me a good 2 weeks to remove all the air from our system and it showed exactly the same erratic flow rates as your chart does. I bled the rads and then concentrated on the AVV on the cylinder. Each time during or after a DHW run I could get a small blast of air out.

Thank you both.

Ouch! Checked the “COP in Window” for the period in the middle and it’s 0.4 :man_facepalming::rofl: