Thank youI had not seen your system diagram before I wrote my earlier post - my posts are delayed / moderated.
No point experimenting with anthracite or air settings.
You need to get your installer back - or engage with Stovax direct who will give you the correct schematic for your scheme and thermal store specification ( albeit you don’t really need a thermal store for a single source installation).
As you will note from the above, assuming your sketch is correct, the installation is wrong (and probably not correctly sized).
Not really what you want to hear I am afraid.
Does it look way off the mark? You have gotten me worried!
Having a look on the stovax info, non of the examples have a separate hot water and heating circuit? Is that an issue.
We decided on a thermal store for various reasons. Mains pressure hot water. Hot water supplied to our third floor en suite planned in the future. We are also hopeful to get some solar panels or perhaps gas/oil boiler (we are off grid) who knows when but thought best to future proof. Starting to regret it now