Battery not discharging when house has significant load

[AliSmi]

Hi everyone

Looking for some advice...

I have 9x solar panels and a FoxESS batteries totalling 10kw storage capacity.
I also have a Grant air source heat pump for both heating and hot water. Once a week I need to run a disinfection cycle through my hot water tank to protect from legionella.
This requires me to heat my water to 60 degrees - from approx 45 degrees. The load will vary from 5.5-3.5kw for approx. 40minutes

The last couple of weeks in the sunshine, I've run this cycle at a time in the day when a) my battery state of charge is at 100%, b) the solar PV yield is 3.58 - 3.7kw and almost no other load/demand is coming from anywhere else in the house.

So my Q: Despite the above SOC and PV yield environment, I'm pulling from the grid (admittedly just a small amount 0.6kw) but why is this happening, why doesn't my 10kw battery start getting used up alongside the PV yield, instead of pulling from the grid?

I have no mode scheduler / force charge set up.

Any ideas/insight would be most welcome.
Thank you

[Will]

If you have a gen2 H1 series or K series you can ask your installer to update the firmware and add -50 watts to the grid compensation setting which means the inverter doesn't draw that always on trickle of power.
I show it off here:

[AliSmi]

Thank you!