Keston S30 query

We've just had a Keston S30 installed in our rental flat - it was the only option that worked for flue routing, and even that was tricky. There's something I can't find answers to in the manual - and I note the online manual is an older version (04/2023) than the printed on (09/2024) one that came in the box :

We've had to change to a sealed system*. Previously the boiler was direct to the open vent thermal store, so worked well - or as well as a 30 year old non-condensing, pilot light, boiler will. But now it's using the boiler coil (and solar coil in series**) in the store, it's just not working right - it's running up the pump to the point where there's a ΔT of only about 3˚C As a result, it hardly condenses.

The manual is "really unclear" on the different modes - specifically there's mention of using SL2 - or "2x Switched Live Operation" as the printed manual describes it. But absolutely zero information on what it does other than allowing different temperature settings for DHW and CH.
If I configure it for 2x switched live, and leave nothing connected to SL2 (because it's not driving any heating loop), will it drive the pump at a more sane speed to achieve a sensible ΔT ?

* The S30 is sealed-system only, open vent is only available on the industrial ones that start at 45kW.
** The boiler coil is rated for 15kW, and the solar coil is very similar, so we've put them in series to maximise heat transfer.

It sounds to me like you've been badly advised on all counts. Obviously can't see the individual installation but in principle if you can get a Keston twin flue system out I don't see why you couldn't get other brands of twin flue system out, and fitting a 30kW system boiler into a flat is insanity.

The boiler won't condense much anyway on a thermal store as they run too hot. Run it at condensing temperatures and your store won't be hot enough to heat your water for your taps, so best to give up on trying to make that work. Also even at minimum modulation it's likely to exceed the maximum requirements of your flat. The pump isn't adjustable either, it sort of is what it is at this point.

It was a very tight squeeze for the flue - anything bigger would eat into something structural (either the blocks of a block & beam floor, or the steels supporting it.) Others I got to look at it either wanted to run the flue through someone else's space, or put the boiler in the kitchen (which is small enough without that.)

I would have preferred to stay open vent, but as I said, only their bigger commercial ones support that. At the right flow rate, you can get a decent ΔT - the old boiler did condense when the clueless ****wit engineer put a TMV in the wrong way round, which didn't do it much good. At the right output and flow rate, this shoukd be able to as well.

As for 30kW, it keeps the shower (or running a bath) going nicely. The store buffers things so when just running the heating, it just fires up as needed to top up the store.

I nearly put a gate valve in to be able to throttle the flow, but the lad installing said "it'll just learn" - which it might do if it was driving radiators.
I'll get their boss back and ask him to get it working properly - I have some leverage as the bill isn't paid yet I was really looking to get properly informed beforehand.