JohnMo

Think I would try to simplify first before adding more complexity. Could you balance the system, so there is always a demand from the radiator circuit? Do this by lowering the flow temperature on the higher curve, so it never exceeds thermostat set point. Think you need to get closer to running as a single zone, so the heat pump has lots of time to settle out the flow temps, and find it's best running point.

Which bit is the holy grail, a heat only boiler, Baxi or smart thermostats. I would say a priory demand hot water (PDHW) running on weather compensation (single zone, fully balanced) was the holy grail for a radiator system.

Viscosity rating. So basic summer and winter grades. Although a lot now has viscosity additives so a single grade is used.

That's how I did mine, one valve per wet room and branched out in the room. Even with shower and sink running hot no issues, no issues flushing toilet while in shower etc.

HVO is almost identical to diesel, except it can ignite more easily. Believe heating oil is just diesel with less duty. You can get if you really want it, but it may cost you more.

You have to be very careful talking biofuel, they can very different things. Biodiesel can be made virgin oil stocks, HVO isn't or shouldn't be. The properties of Biodiesel and HVO are also very different.

I would ring the manufacturer ask them if the parts are available and help diagnose the issue. Generally the units are pretty easy to repair.

There are several troubles with HVO. Basically it should be made from used (and only used) vegetable and animal fats/oils. Sometimes virgin oils and diesel make their way into the mix. The transport industry (roads and marine) are using it as is industry, all from a defined quantity of used oil world wide. Several years ago the EU (incl UK) apparently imported many more million tonnes of used oil stocks, than was actually available. Where did this come from - no-one knows. But it was sold as hvo. Most stock of used oil is from Malaysia, all of which is palm oil from deforestation and is a mono crop, not good for biodiversity. The process for making hvo is very energy intensive. Combustion produces all the same pollutants and PM 2.5 etc...as diesel, but credit is taken for CO2, even though the CO2 is sucked up in Malaysia and when burnt in Europe is just more CO2 dumped into this part of the world So a lot of green wash, from a defined amount of material worldwide, that everyone wants to take credit for. It's available to buy if you want, I wouldn't bother.

Think they would be more suited to something other than an ASHP. Keep it simple UVC, with a large coil for good heat transfer at lower temps, so about 3m2 coil or bigger. If you only have UFH, you really don't need a mixer/pump, let the ASP circulator do the UFH directly. Then you just need a diverter valve to direct the flow to UFH or cylinder. Lots of variables Do you get paid for export? What do you do when the battery is full? I had a diverter, but had two fail, so skipped the idea of paid for diverter. I use home assistant and do two things. All I needed was one Shelly relay (second operating point for ASHP switch) and one SONOFF High Power Smart Switch Power Meter Switch (POWR3 for immersion), so about £70 all in, and does a way better job when you have a battery. ASHP - have a second operating point set up, so when battery is 97% full and generating xkW, the ASHP is started - generally get a CoP of 4 or above, doing this. Second if the battery get to 98% I power a relay to divert to cylinder immersion. Leave both to run until battery drops to 95%. Then stop both processes two hours before sunset, so battery can get to 100% or close to that.

Yes the bottom layer of blocks is just normal concrete blocks. No condensation. Just done a couple of thermal images The door sill is aluminium, outside is 5.5 degs. Aluminium is showing 13.3 degs, but never seen any damp. This is our lounge window, done the same way as doorway - the window goes to the ground and no aluminium threshold. In the same area it's 19.1 degs.

Break it down to clear decisions Radiators yes or no. You need to do room, by room heat loss calculation, choose a max flow temp, then decide can I live with size radiator? Assuming not move to UFH UFH you need insulation under it. Ideally the equivalent of 150mm PIR, to enable low flow temp. Can you do that with the existing floor make up? If not dig out and down. Will not be cheap and you will have to pull house apart. Third option could be way easier and cheaper. Insulate to best best bang for the buck, look for air leaks and fix - all pretty cheap. Address how the building is ventilated, which is missed by most. Either fan coils with A2W HP, or A2A heat pump. Both options allow small heat emitters, A2W would be sized to use a max of 35 degs. A2A would be better a working solution out the box, one outside unit and multiple indoor emitters.

Never did, but still managed an engineering degree. But can't spell to save my life, so badly sometimes that spell check doesn't help either, so have to use a different word altogether. Surprisingly putting really badly spelt words into Google search, prompts you with the correct spelling, even thought spell check has no idea.

✔️ nearly Thermolite level with top of screed, so no gap where you show ? Level threshold sits on top, then tiles level the whole lot.

Dyslexic and spell check are good friends sometimes.

They are on their edge, you have drawn on the side, flick them over 90 degrees, so threshold is about 215mm wide As shown previously

No, on edge, one behind the other.

Possibly a rectorial question - but no they don't. They are taken for the mugs they seem to be. Money rich, but that's about it.

What nonsense. You need DHW however you heat. So assuming a system boiler Cylinder needed for both gas or ASHP - zero cost. Central heating needed, UFH is the obvious choice for any new build, no radiators taking up wall space. UFH same for both ASHP and gas. By default you end up with same plumbing. ASHP or good WC system boiler, pretty much the same price, so no idea where the £7.5k uplift in costs comes from. Vitodens 200-W 11kW System Boiler can be around £2k (recommended price over £3k), Daikin 5kW ASHP £2k. Funny thing they come out at the same cost.

Just been going through some photos, I actually used 2x 100mm thermolite blocks at threshold (not one, stated previously and 70mm upstand.

The wall is ICF, the wall make up from inside is Plasterboard 50mm batten 365mm thick ICF block (concrete is inside and insulation outside). This is the sub DPC buildup for the walls, upstand not shown. The upstand at the doorway basically gives continuous insulation around the building - below floor level cavity and across doorways

Will let @Nickfromwales comment on the merits of Ivar mixers

Pretty much that, all done with level thresholds. We have 5 doorways all the same design. Tiler used extra flexible adhesive over the PIR. And we used large format tiles

It doesn’t specify as far as I can remember It does Unless otherwise indicated by the manufacturer, a carbon dioxide monitor, with or without an integral detector, should be mounted between 1.4m and 1.6m above floor level. A carbon dioxide detector head (or monitor if integrated) should not be sited within 1m of the expected location of a bed-head.

I did 70mm, (but walls are flattened 50mm plus plasterboard), they go from the bottom of the floor insulation to floor level - top of screed.

If you are doing UFH strongly consider 150 to 200mm PIR or 300mm EPS. Wall is woodcrete ICF, concrete, lime parge coat inside, and breather membrane behind wood cladding.