JohnMo

That really depends on your starting point. There gets a point where return temp doesn't really get much lower, especially with WC when heating at 10 degs outside. Return temp can never drop below room ambient, even if it got to ambient, rads would be huge. So practically you are at min return temp already. Getting a bigger dT is just increasing flow temp for no reason. If you lowered your return temp any more, your 4 degrees delta for restart would never be reached or take too long.

I'll nip into town later and pickup some proper centre clamps. Will struggle to correct the LH side clamping zone. Some of the clamping zone will take some thinking about. Prevailing wind is directly on the front of the panels. Any wind from behind sails straight over the panels due to the hill.

We used copper. You don't with nails either.

Clamping areas are the same as the last panels they were ok in 80mph+ winds. Yes two strings to independent MPPTs.

Pretty flawed heat loss calculation you should have done it at -3 outside and 20 inside, but your boiler is still ok for that. Your just fooling yourself with overly small heat losses and too smaller range rating figure. Range rating to your calculations for heat losses at +5, what happens when you get a zero degree day, and your house drops to 11 degs? Because your boiler output is too low. Think I would rerun the heat loss calculation for realistic figures and range rated accordingly. First alarm bell is this. If you letting the house get cold (16 is cold in my book and that's your target temperature), the boiler needs to run balls out (especially when range rated right down), so may actually be struggling. Taking a long time to find a comfortable running point. To get a house to 16 with radiators in 2 hours is a long time. For me You have range rated too low You allow too much set back when heating is off - at a target of 16 why would you set back at all. Just let the heating run 24-7. Let everything stabilise. Your boiler will start to run more efficiently and modulate down on its own. Range rating is good for stop start heating as it allows a level of heating output more suited to the house at startup, but you have to careful, analogy If you are trying to fill a bucket with a hole in it (your heat loss), the hole allows 10L per minute to leak out. You open the tap (your boiler) and it flows at 10L per minute you will never fill the bucket. Open to 11L per minute it going to take a long time to fill. That is where you are now. Boiler running hard for too long.

Why not replicate the existing house with wood fibre IWI? Not a fan, too easy to make a dogs diner of it, and effectively make it useless. Disadvantage of IWI is you make the build thermally light, so temperature can yo-yo over a short time frame. It very limited thermal capacity. Or just go with a bigger cavity, heavy blocks inside and out, and either poly bead or mineral wool or similar cavity fill. Then just plaster, not sure what the parge cost brings to the party if your plaster anyway?

Me neither, every start equals wasted heat out the flue and stabilising metal work temperature, instead of real work heating the house. Long runs equal efficient use of gas.

You would drive down your pumping losses with a wider dT. But suspect they are low anyway. Your current mean temp is 29, the 40-28 drives your mean temp to 34, wouldn't you start to over heat the house quite quickly? To run 12 dT, and keep the same dT across the radiators wouldn't you be closer to 23 and 35? That would give an additional 3 degs of condensing and about as low as you could go. But whether you could actually get that low in practice is questionable, not sure you would ever get a permission to restart after a heat cycle, as return temp would never drop low enough. My Atag, with it's modulating pump and 32 flow would have been running 4-6 dT, like it or not.

Maybe simpler to do it upstream of the combi rather than after. Then small amounts of temp rise give massive uplift in flow rate. Combi-SuperFlow-White-Paper-v1-2-4.pdfCanetis-SuperFlow-Product-Sheet-WE-050318.pdf You can also do it way more cheaply than a mini store. As a mini store is based on heating medium in the cylinder and domestic water in the tubes. So you really need to connect the combi to system boiler for the proposed to work.

Why would you install with a gas combi? Tell us what you are trying to achieve?

Unistut copy from local electrical factors (Medlock), comes 6m lengths.

I would want a number, otherwise it's meaningless. Getting towards something is very open to interpretation, scoring 6m³/m² @ 50Pa is getting towards passivhaus (it's nowhere near) compared 10. You possibly thinking under 1.0, so there may or may not be a big gap of expectations?

Steelwork modified, using 41mm square channel, two panels in place. New array

Call your installer

Panels now upgraded, photos tomorrow. Day one, took 12 panels off the hill Day two, very windy, modified the steelwork for new panels Day three, new panels lifted up hill and installed, reused all old wiring without issue. Switched it on and all worked fine. Materials 2x 6m lengths of 41mm galvanised channel 12 panels 28x 30mm panel end clamps.