I would start by downloading the correct Kensa manual it will answer your questions in the most part.

Are you radiators or UFH or a mix?

Buffer or no buffer? If buffer did they follow Kensa plumbing schematic of a two port - so only two port connected one at bottom and one on top?

@johnmo I have the manuals - installation and user. Not necessarily the most user-friendly or aimed at system optimisation. I'll be calling Kensa once I have the handover pack and know what I want to ask.

All radiators. We had four upgraded.

100 litre buffer - 4 port configuration, which, to be fair, I have seen Kensa articles that recommend both 🙄 

Welcome aboard, and first off, well done for pushing through. Sadly, your experience isn’t unusual, and I completely agree: if every household had to navigate the chaos you’ve just been through, we’re in serious trouble on the road to decarbonising heat.

You’ve raised all the right questions, and yes, a couple of alarm bells are ringing for me, especially around the weather compensation. When both the plumber and electrician say “you don’t need it,” yet it took you being annoyingly persistent just to get the supplied sensor fitted… that’s not a good sign.

Weather comp is essential for efficient heat pump operation… especially with fixed-output GSHPs like the Kensa. These systems benefit massively from gently adjusting the flow temperature in line with outdoor conditions.

As for “treat it like a boiler,” that’s another red flag. If you run it purely on on/off thermostat logic like a gas boiler, it will short cycle itself to death in shoulder seasons. It needs a different mindset: continuous, low-temperature flow that matches the building’s heat loss. You’re absolutely right that the 30C return and 35C flow is just for the mild months, but as outdoor temps drop, the curve should scale that up, automatically, which is exactly what weather comp is for.

Just had a quick scan of the manual and should be weather compensation enabled, so this is the correct mode to select.

Posted by: @algienon

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How do I set up weather compensation?

It's in the manual. But set min flow temp at 20 degs outside temp, then set your outside design temp at say 45 for a start. Then every 24 hrs tweek design day flow only down or up based on indoor temp.

Posted by: @algienon

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There is a 3-way valve from the heat pump that feeds the CH and DHW. I'm guessing that although this allows both to be served at once that this is not optimal and I'd be better using the timers to deconflict each demand.

Your system will run what is priority demand hot water. Hot water will always have priority over heating. The heat pump control will manage flue temp for cylinder heating. Just schedule to heat a couple of time a day at most 

Posted by: @algienon

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So we have a secondary return (SR) fitted to pre-charge the hot pipes in the house before the morning and evening rush.

The way you have set sounds about correct. Just make sure the time suit you.

Posted by: @algienon

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Should TRVs all be opened to the max or can I use them to drop the temp in the bedrooms?

Yes and yes