JohnMo

Effectively completely ignore the GSE instructions, they are not applicable to a sarking board roof. Attach the trays direct to the sarking, through the membrane

You have self balanced actuators, maybe it was just going through a learning period, some can take quite awhile. With SQ610, you have a setting that optimises control to the Salus self balancing valves. Go on to Google and search for the full instructions for the SQ610, not the quick guide that comes with the thermostat.

Buy the correct aluminium capping pre made. You will not get a sharp bend without a proper bender, and depending on grade of aluminium it may crack.

So do you have an issue?

Not sure I would ever hand that over to someone - what you actually want and they will assume is ok for will be very different. Do your own leg work. Get the right architect they will handle that for you. Turnkey and to first fix are very different. Turnkey you give them an empty site, you then move your furniture in. First fix is generally before any plasterboard has been installed. Lots of work to do after 1st fix

Long reply Sorry it's huge. You need good modulation at the 7 degrees point. But it only modulates down to 4.32kW at 7 degs. Our winter average temp is around 7 degs so your heat pump spends most it's time in that range of output. Your heat demand at design point is lower than that. But their next size down, in real terms, is too small for your demand. So you will get cycling and have a hard time setting it up. Your scop is likely to be high 3s. But if you get a more appropriate sized heat pump your SCoP should be low 5s to mid 5s. My current heat pump is 6kW, but since purchasing I have found it's actually a software limited 10kW, modulation is similar to the Cool Energy unit. I have got it running acceptably, but it's just took big a mild temps. So that has a few impacts - Your target flow temperature is higher to make up for cycling. It was 7 degs yesterday target flow temp was 29 degs, cycling was 40 mins on 90 mins off. So I got a cop associated with a 29 Deg flow temp, CoP yesterday was 4.6. However is it didn't cycle and ran steady state, flow temp target would only need to be 23 degs and CoP would be closer to 6.3. A saving of 2.3kWh as a good estimate on one day.

Guess I should have looked at the spec correctly - yes 25A, not 100A.

Two basic models, WQ610 is for radiators and SQ610 for UFH. If you have a WQ on UFH and you have any self learning functions active, the thermostat loses all control as the algorithm is wrong for the application. A WQ will work with UFH, but only if you use in a simple on off mode. Been there, done it, got the tee shirt.

I have a SONOFF POWR3, it will do a 100A, so driving an immersion is a walk in the park. Have in parallel to an immersion time switch. I used for PV diverting. Pretty quiet, will connect to home assistant if you want.

A GivEnergy AIO comes with a default setting of ECO, this can be switched on or off. Turning Eco Off requires you to set specific Timed Charge, Timed Discharge, or Timed Export schedules. So set eco off, you can set the charge during a cheap period and set a timer discharge this would discharge to house until flat or time window has elapsed. It would ignore PV so it would all be exported. Once battery is flat it would remain so, ignoring any PV until next charge window. You can also schedule a discharge to grid. This an AC coupled battery

Which quantum model? There is one for UFH and one for radiators. Do you have self learning stopping starting on or off?

I would check the thermostat settings and your controller. If rooms are 10 degs and you have the thermostat set at 8 degs, where is your boiler call for heat coming from. More details needed

Should that read UNWISE?

Trouble with a lot of MCS installers they simply ignore all improvement made to building fabric. They then apply a huge ventilation heat loss if you're not careful, then add a bit just in case. As said by @crispy_wafer do your own calculations make sense of everything in your own head. I recently asked about a heat pump quote via an umbrella scheme, they had my EPC, my house drawings, quoted a 12kW heat pump. I have just bought a 4kW, without grants.

The normal run of things You charge on cheap rate, battery depletion starts on expensive tariff. As PV generates it go to charge battery first, then when full, any excess not be used by house, goes to export. Any variation from this is robbing Peter to pay Paul.