JohnMo

I used this one also, have to say it is very good. On 10 degree days, it does say you need more heat that you actually do, but doesn't account for people or solar gain. However the last 24 hrs, with an average temp at about -6 and no solar gain, almost to the kWh over 24 hrs correct. Can't ask for better than that.

I would switch off the stop cock, but leave heating on low, say 17 or 18. Drain down the cold drinking water pipes, wouldn't hurt.

Nothing wrong with that, but they don't preach to bin all the thermostats, they do say to set your thermostats above your target temperature as limit stops though. Not really sure that's hardcore. They do say to limit the amount of zones you have, for a heat pump that keeps a large capacity of water available for the flow rates a heat pump needs and helps stop short cycling when heat demand is low. Limiting zone and using thermostats or Trvs at above the target temp are both things are exactly what what my Atag boiler manual says if running WC.

I would leave pump speed alone, just adjust one variable at a time. More flow is more heat, less flow less heat. Interesting that your reading room has no flow, or very little in the photo?

Trouble with small you can't put the kettle on. We got one of these for £800 (now £1000) P1PE 7.9kW / 9.8kVA* Recoil and Electric Start Site Petrol Generator (Powered by Hyundai). One these to switch mains over to generator £38. https://www.amazon.co.uk/gp/r.html?C=2X8R0PK3LTH9J&K=34MIE1U6GOBVK&M=urn:rtn:msg:20220215092805432dc27e9784454aaa817bf54550p0eu&R=3L1EKYM8H7V8M&T=C&U=https%3A%2F%2Fwww.amazon.co.uk%2Fdp%2FB079Y3PJN8%2Fref%3Dpe_27063361_487055811_TE_3p_dp_1&H=F0W7TJ2VHJTNC41TRU0YCSGUQ4SA&ref_=pe_27063361_487055811_TE_3p_dp_1 You would just need an LPG conversation kit.

I have a combi, and tried running DHW at 55 degrees, routinely used 8kWh of gas on DHW alone, no CH on at that point. That was with some water preheat upstream of the boiler. Long story short, I ended up setting the DHW to 65, then routinely used 6kWh, so actually saved money. Not sure if that's because the boiler has flue gas heat recovery and upstream preheat also. Central heating, I am charging a buffer to 32 degs, flow temp max is set to 50, but generally doesn't go past 45 flow temp, with a return mid to low 30. Have energy meter just prior to the UFH heating. Monitoring the energy use, both gas and at the energy meter, shows an efficiency of converting gas to heat of 95%.

Go on to heat geek website read up on weather compensation, zones and system balancing. Spending a hour of your time, read and watch the videos. Get some basics understanding and then most of your questions will answer themselves.

ICF build, except the top of wall behind the cylinder which is timber frame. Walls 0.14 Floor 0.09 Roof 0.11 Windows 0.6 to 1.1.

I am actually using a combi thermal store, mainly because I got it new very cheap. It is indirect with a coil inside. The coil is way too small for low flow temps (designed 80 deg flow temp), so have added a large 40 plate PHE and pump. In the summer it is charged by excess PV and goes a long way to reducing DHW gas usage. Photo prior to and after insulation

Will do low 20's Only goes down to 6.7kW at low flow temps, 6kW at high flow temps. Hence the need for a buffer. But DHW performance is why a bought it, 95.1% efficiency with flue gas heat recovery built in, 18.8l/min flow rate, using the buffer with a preheat coil in it. Will run two showers with ease and third if you are careful with temperature setting. It's not peak load that kills you with CH, it is low load short cycling. Have reduced last years gas consumption, by a considerable amount. Using big buffer is key. October 800kWh reduction (561kWh this year, 1370kWh last) November 600kWh reduction (1138kWh this year, 1753kWh last year) December looking to save over 1200kWh

I have a Atag A325ECX, super quite

Assume your heat load is at lowest temperature. So it will also need to 0.5kW when it's about 10 degrees. So basically you need a buffer. A decent combi of your choice with a good sized buffer. My heat demand is just over 3kW, boiler lowest modulation at low temp is 6.7kW. Have 180l buffer, with a thermostat set at 34 deg. UFH just draws it water from the buffer and pumps around UFH at 30. Currently getting 94% efficiency from the system - Gas in to heat water to heat taken from UFH via a heat meter.

Do you still have the fine mesh behind the coarse mesh?

On the Ivar mixer, the part that connects to the hot part of the manifold has an integral isolation ball valve, have you checked this is fully open? Needs an Allen key to move I think.

Is there any hydraulic sepereration between the pumps? The buffer would normally be the hydraulic sepereration, the manifold pumps pulling/pushing from the buffer. The one in the middle of the buffer and UFH pump may be the issue It could be you have too many pumps. Can you switch of the buffer pump and see what happens?

Questions Are you running this on a single pump between the buffer and both manifold mixers, or do you 3 pumps, one on each of the manifolds and another at the exit of the buffer?

I may be wrong, but the coil sizes in the brochure look small for a heat pump? Could be a custom build heat pump cylinder with a larger coil, hence the slightly higher over all capacity of the cylinder?

Couple of things Bigger DT means lower mean temperature, which means lower output. Mixer like the flow temp 10-15 hotter upstream than downstream of the mixer. Boiler condensing is a function of return temp not flow temp, if your return temp is below 53 deg your are condensing. You say it worked, then you changed stuff, put it back the way it was. If it reaches temp, all good. Then change things one at a time. If you reduce flow temp, to get the same heat out the floor you DT needs to reduce. If you decrease boiler flow your mixer may need adjusted to keep.the same floor flow temp.

Maybe it's not level

Sounds like you have the flow temp set too high. The floor response is such that you are overshooting the thermostat. How thick is the insulation and screed, what flow temp?

The other issue maybe you are just running the UFH for to shorter time, running longer may do the job without increasing the flow temp.

You are living in a barn and you have left the doors open, or your heat emitters are undersized. But looks like a controller suitable for both a heat pump, but also a gas boiler.

I had so called self learning thermostats, but they just couldn't cope this the heat up and cool down times of thick screed and low flow temp. So next to useless. House was to hot or way to cold never the correct temp. So got used as on/off.

Not really clear what you are asking? All really depends on what state the house is in, if you are living, showering in the house mould could be an issue, especially if not heated also. Or if there is no real humidity being developed, mould issue not really there. If you are building and living in property a good chance the duct work will end up with a good coating of dust if you start the MVHR. If you are heating and living, I would crack the bedroom window open at night and open a window after a shower and take a hit on heating costs until building work is complete. Better than filling MVHR ducts with dust.