JFDIY

The blurb refers to a super capacitor.

Tidy.............I can hear @Onoff tearing his hair out ?

Good to hear this, I went down a rabbit hole yesterday with a kitchen tap, absolutely impossible to get to tighten the flexi-tails with a spanner, even with the tap stripped to its barest form on the bench, the flats were in-accessible, after some head scratching and rationalisation I came to the conclusion the O-ring would seal whatever the applied force and reasoned hand tightening would be good enough. Good to have it clarified though.

If the loft hatch was anything to go by, I think the internet isn't big enough to cope with the amount of pages the thread might take

I made the same mistake as your builder on a couple of external corners/piers, but I only realised it once I was further on.and no height to really cut and shut things which would be the easiest and ironically the best thing to do. In my case I'd used really heavy gauge DPM and was able to blast the area with a fan heater and hot air gun, then use a piece of wood with slightly rounded edges to manipulate the plastic into the corner, then hold it there while you take the heat away. It wasn't perfect, but got it formed to a much more acceptable margin that a tile overhang and some skirting/beading will cover. In your case I'd do as nod suggests, when you get the floor DPM in, you can then cut at 45⁰ into the corner and tape to form the proper shape.

If it is air locked , and a there is a high probability of that, you really need to be considering putting a couple of auto-vents in on the high point of each loop, save the frustration of a repeat issue. Which will most likely cost more now, but save it going forward

There either should be some air vents to bleed any air, or if not there needs to be some way of getting air from the loops. There are ways to do this with a mains pressure hose, but it isn't a serviceable system without a means to purge any air.

Is the manifold located upstairs or downstairs? And is it the only manifold? Is it on the same floor as the issue?

Was the thermostat knackered from the start? Or in the wrong place, did the heat pump get a signal to produce heat, all seems rather coincidental to me.....

Think I suggested feeding the cistern with hot water. I've had this set up for 10years in my bathroom. It's a TMV fitted after the hot spur to the basin tap, TMV set at around 25-30⁰ (basically water in a hot summers day) When you repeatedly flush the toilet the water in the cistern is best described as tepid. I get no condensation and the water you'd normally waste down the sink is mostly eliminated. I intend to do the same in the kitchen on the feed to appliances, to speed up hot water availability at the tap as the kitchen is a long way from UVC and it reduce cycle times of the appliances + cost of heating the water with gas v's electricity is cheaper

I got some Domas DDseal from my electrical wholesaler without too much trouble. If memory serves it seemed to be the only thing that was specifically quoted as being suitable for PVC and metal. Other products I found only referred to metal ducting.

Wickes were cheaper than TS, if you have the 10% trade card they're £13.41 for a box

Think you should ask for your money back!

If you've got a slab to work off, get some scaffold up and put back as much as possible pronto, even if you have to support beams in fresh air on the scaffold. I had a oak framed barn with permission for conversion that had been re-newed many times over 15years, eventually we made a 'significant start' elsewhere on site and another 5 years went by before I asked about what might happen if it fell down. The planning officer I spoke to said make sure it doesn't happen or you have nothing to convert. I asked how much I could take down at any one time, I was advised one element, which seemed unreasonable, but was suggesting one wall or the roof covering but not both at the same time. I put in place rsj's internally with artic trailer 'landing legs' all set up to be able to take the weight off each wall one at a time if needed. Then a neighbour had a massive extension/rebuild granted and I used this as precidence to get a planning submission for a rebuild , but I was prepared for the long haul. Made taking it down easier and safer anyway.

My go to is loctite 55 instead of PTFE tape. Bought a small packet last year and every joint I've made ( around 20 or so ) with it has been leak free first time. Could rarely say that with PTFE, oh and on that note the gas rated PTFE is thicker and better in my opinion.

Excellent, does this still involve the remote sensor to the rear of the backbox, or using the internal one built into the thermostat faceplate?

Have you considered smashing a load of holes in the white backplate, then spacing that off the wall (if needed) to get airflow

What about making a spacer plate to sandwich behind the stat and protrude below enough to house the sensor. Could make from acetal or white perspex sheet and polish the edges to look decent.

Mate of mine has a scruffy hi Viz jacket he always puts on when he goes to buy anything. If you look like you have money some places will pick a price accordingly.

The wickes one is worth doing (assuming they have a branch near you) 10% off for making up a letterhead and business card for Joe blogs home improvements. Surprising how competitive they are on some things and how handy out of hours so might as well get a bit off. They're owned by Travis Perkins yet offer better than TP's price on some things.

Definitely lag the cold to kitchen, nice to have cool(er) water when making a glass of juice/water in the summer

How often are you likely to need to change the individual room temps? Just wondering if you can use the in-riom locations for a remote sensor and move the 'stats to the be next to the wiring centre at the other end of the cable? Though you might be then into a calibration exercise due to cable length (resistance) shifting the remote sensor output. You can get sensor enclosures reasonably cheap, bit like these; https://evatron.com/enclosures/sensor-enclosures/en30w-sensor-enclosure/

I think it's the same as a grundfoss/reliance thermoguard mixer setup, notes are available, but the return loop to boiler and cold manifold are common with no valves and can be fitted either way. Does the boiler pump stop and just leave the ufh pump going? What do flow meters show for the loops in manifold. Something is being 'dead-headed' and causing chatter. As mentioned by others above a stethoscope approach with a piece off wood or large screwdriver to your ear and suspect parts will help you find what is making the noise, but this may well not be the cause of the problem. I still wonder if you have rads elsewhere if one is open, or if you need a differential bypass valve in the system.

Had another look and I think the valve might be ok, be good to get the pukka JG notes though. How are the motorised valves configured, are they shutting before the pump has finished running? You may be able to hold the one serving the manifold slightly open if it has a manual lever ( don't latch it as you'll make unwanted electrical contacts inside it). See if when the pump is noisy moving the lever to open the valve off its seat, stops the noise, if so the pump is being starved of incoming water .

Think your blending valve might be in the wrong way, not sure it makes a difference without a schematic or installer notes, but it spears the boiler connection to right in the middle of blending valve should go to the cold side of the manifold. Attached photo from JG website shows the issue, all the pictures I could find show the manifold configured with pump to the left. If you spin the mixer so the dial is pointing towards the wall it would be more as designed. ( Space permitting)