JohnMo

Why - Computherm are way better, you just need to control on a single zone, pump controlled by thermostat. Thick screed doesn't need remote inputs from work, it needs to run continuously to batch heat (4 to 12 hrs) depending outside temp and flow temp, or continuously at a low flow temp. Why what are they going to do? If your floors is getting to 26 your flow temp is way to high and you are trying to do things too quickly, without knowing anything about your house, suspect you flow temp should be in the 26 to 30 (continuous) or 35 (batch) range With a 140mm floor thickness if you are getting hot, it has taken you 24 to 48 hrs to get there, you ain't stopping with a floor probe, way to late. Example, my heat pump is set to a target flow temp of 35 degs, after 12 hrs of running it's flow temp is 33. Would take me another 12 hrs to reach the flow temp of 35. The floor surface temp when I stop heating is around 22-23. You have 50% more floor height to heat up. Your floor will be super slow to do anything.

Generally ok, but could be rubbish, depends on make really. Ivar good and very adjustable, ESBE electronic good, most other not so good. Set the flow initially to match the pipe length and adjust up and down there. Plenty of calculators online. Thick slab is best heated by batch heating to a very low (0.1) hysterisis thermostat, or running continuously, all on a single zone.

Not sure how you would be allowed to do any work yourself, as the work has to be done by MSC contractor to get the grant. All things being equal the cost delta on a new build is the difference in cost between decent boiler and heat pump, everything else is basically the same. So really should be £1000 or less. My cost delta if I hadn't installed the gas boiler first, would be around £500.

Sorry slightly off topic, really consider an ASHP. My build started with a gas boiler and although not passive, getting the gas boiler to work efficiently in a low energy demand house isn't that easy. Our max heating demand is 3.5kW, but most the heating season you need less than half of that. Had two heating seasons with gas boiler and then self installed an ASHP. We have plenty of solar, battery and on E7, but even in Dec and Jan when solar is rubbish the ASHP is cheaper to run than gas. And it's easier to get running well on low heat demands.

Bad idea - You would have to very careful doing that. Would need to be copper or stainless and very clean, otherwise it would not be healthy to drink the water later. And certainly don't want to get carbon steel corrosion products in you unvented cylinder as you start to get pin hole corrosion in a couple of years. We had an 1830 build last, that had a cold room, thick stone floor, walls and 50mm thick stone shelves, never changed temperature year on year. A passivhaus doesn't necessarily mean exactly the same temperature everywhere. Really depends how you build the space.

So to be pedantic, it's not fully installed. Not sure what temperature you currently have, but we had -3 the other night and a few nights hovering around zero, snow and sleet yesterday, -2 tonight. So the system will generate plenty of condensation, if only half insulated.

My view is install fully, then run. Don't run part installed.

I would expect it's a secret. Localised reduced bore has little real effect on system pressure drops, if you do the pressure loss calcs. Would think there will be a pressure drop table in the install manual, just a matter of finding it online.

How are you trying to set it up? What flow temps and for how long etc? Big heat pumps are really best run on weather compensation or a low set flow temperature for very long periods. Do you have lots of zones, buffer cylinder, explain your setup?

Looking good. Nice to see it's able to run constantly at 25 degs.

After quite awhile messing with WC, I actually find it cheaper to run a set flow temp of 35, and let it run as long or short as required by a 0.1 hysterisis thermostat. Low heating demand and WC doesn't make that much difference, my curve was something like 0.3 per Deg OAT starting at 10 degs down to -5. I get a consistent CoP of just over 3, but only because I make it heat during the night when it's coldest - because my tariff is cheapest then. Bathroom towel rails, we did electric. If you do UFH in bathrooms cram as much pipe into the floor as can, as floor surface area ends up quite small. If you want to do intermittent bathroom heating the output needs to quite a bit higher than you think you need. Especially if the ensuite if attached to bedroom at 16 to 18 Deg.

You said earlier that the aga had an external air feed? If that is the case it doesn't draw air from the house. So the ground floor only has a utility fan that is light switch activated with no over run timer? And upstairs only one fan that is actually used. If you aren't replacing air and you are developing humidity your house will get damp.

So your only forced ventilation for the whole house is a single bathroom fan. So you really need a fan in the other bathroom and kitchen. The Greenwood ones mentioned can be really from eBay. Adding a humidity activated trickle would ensure the cross ventilation is occurring when and where needed. Example bedroom vents normally closed in the day opening during the night when you are sleep etc.

Why? Bit like leasing your TV in the 70/80s, 4 years later you could have bought it twice over.

For new builds it is already cheap enough, unless you insist on paying a premium for a Vaillant heat pump. The UFH should already be being installed, so it operates on very low temps, a cylinder is most likely being installed, then the only cost added is the difference in heat source price. A new build should almost never need a heat pump above 8kW, most a 5/6kW is bigger than really required. Plenty of decent heat pumps on the market for reasonable price. Retrofits are always going to more expensive, with microbore and or small radiators etc. to contend with, they should get the grants. A heat pump should really be made mandatory for all new builds anyway (without a grant) and any other reason you need planning permission. If you don't like it, don't do the new build or extension etc.

Biggest joke is it says the same for wind turbines, bet there aren't any MCS installer, as there are no grants. Once grants stop, there will be very few MCS heat pump installers either.

That fan looks ideal also. Set to run continuously, with automatic humidity sensing and you could minimise the overrun timer as the unit would look after itself. However 10l/s isn't enough to ventilate the house. I had a look and the AGA requires a 30cm2 air inlet grill permanently open, is this in the kitchen? Your ventilation strategy will have to take account of the air requirements of the Aga so you don't start to depressurise the house.

Get another quote, the guy obviously prices as he doesn't want the work. Speak with octopus or other utilities provider they all install heat pumps under MCS.

I will jump in on the ventilation issues. You currently have from the sounds of it, an intermittent high flow fan in the bathroom, you shower or bathe and ensure the door remains closed until the fan stops. You have trickle vents in the windows. Plus you run a dehumidifier. First have I missed anything? What other wet rooms (kitchen, utility, toilet, shower rooms etc) do you have and how are they ventilated? What temperature do you keep you house at? Trickle vent as useless on their own at ventilation. Intermittent fans are great at short term moisture clearance issue, but do not really provide a sound ventilation strategy for the whole house. For this you need a continuous supply of fresh air, ideally controlled so you ventilate as much or little as required. It works but continually blows cold air from the loft or outside or heats it via an electric heater element. Not an ideal solution. Cross ventilation has been shown to work well. For this you need continuous running extract either a central unit (MEV) or room dMEV fans in wet rooms and trickle vent in dry room (bedrooms, living etc). Plus door undercuts so air is free to move when doors are closed. Add to this humidity sensing trickle vents and humidity boosting on the fan. Greenwood CV2GIP dMEV fans are excellent, silent in operation automatically boost on humidity require 2-4W electricity. In addition to the above the house needs to warmer than the air it pulls in from the outside.

Simple flow chart to diagnose issue. When was the last service completed? You need to know what you are doing with UVC get a certified (G3) person in to sort it out.

Plus even with 100mm insulation you will still be loosing plenty of heat downwards.

That's a very good point. May be better buying different lengths than 100m or planning the loop layout, so you get to get 3x100m loops. One of my loops does half the hall, main shower room and kitchen diner. Then you only need to 3 port manifold.

I didn't and building control weren't fussed.

Dump the hard wired thermostat and get a wireless one, so you move to best position once you get the system commissioned. Use a 0.1 Deg hysterisis thermostat, like a Computherm Q20RF (from Amazon). Thick floors take many hours to respond. A normal 0.3-0.5 Deg hysterisis leads to big temperature swings. No need for a floor probe, adds nothing if your flowing low temps. If you are going to use a mixer get a good one either IVAR (low temp one) or ESBE electronic. What do you need the isolation valve for? Just switch the pump on/off via the thermostat. The flow is pulled through the mixer, once pump stops so does flow into the floor.

PTFE and screwed connectors have been the biggest area of rework on my house. Have now dumped using PTFE completely and now use Loctite 55 sealing cord. Easy to use seals first time, every time I have used it.