ProDave

The only thing I can pick out from that poor diagram in the manual is that it is expecting terminals 1, 2, and 2a to be used, you only have 2 wires. I wonder if it is expecting a changeover contact rather than an open / close contact? Other than that, if you are SURE the contact is opening and closing (measure the voltage between terminals 1 and 2, relay closed =0V relay open = some higher voltage) then it has to be some setting needed to tell the HP to use the external thermostat. What does the installer say?

42 degrees is not very high. Where are you and what is your outside temperature? The worst for icing up is a few degrees above 0. Is this a new system or has it previously worked okay in cold weather? Is the big air fan on the external unit blowing properly?

So you are putting as much heat in as you can constantly, and the temperature in the room has dropped as the outside temperature has dropped. So as @Radian said above you have reached thermal equilibrium and this is as hot as the room is ever going to get with this outside temperature and the UFH system you have. All you can really do is supplement it with some other heat source in the very cold weather.

What are the details of the building? Insulation levels, calculated worst case heat loss etc? As a trial, remove the actuator heads for a while, this will let all loops run at maximum flow rate uncontrolled, if that can;t put enough heat into the house then it never will.

My question remains HOW does the external controller "call for heat" from the heat pump? I would assume a wired connection probably to a volt free contact. I feel this is the bit not working but you have not provided any details yet of how the external controller talks to the heat pump to call for heat.

Yes I believe the case length is overall length, how deep the hole in the door needs to be, and backset is distance fromt he door edge to the centre of the spindle.

Kitchens will be harder to heat with UFH than most other rooms because when you take out the area under the kitchen units and under the fridge, you could well be down to not much more than half the floor area being heated. We notice the same in our utility room that it is the slowest room to heat up, but it does not bother us as it is never "cold"

So that zone is not switching off. Perhaps that actuator is wired to the wrong zone or it is simply not screwed down onto the manifold properly.

Not what I expected. Under what planning rules are you building this? To be a "caravan" in UK planning law it needs to be moveable. That looks built very close to the ground, I don't see how you could ever move that. What sort of foundations is that on?

You will have to disconnect say the blue from the existing frost stat and add the pipe stat in series, requiring an extra terminal, e.g. a single choc block to make the joining connection.

Ne technical reason, all mine are above the manifold in the walls or ceiling void. I would be asking why he wants to keep them below the manifold.

As the title says, the amount the DNO can charge for renewable export network upgrades should reduce next year. https://www.cms-lawnow.com/ealerts/2022/06/distribution-connection-charges-to-be-reduced-ofgem-publishes-its-decision-on-the-access-and-forward Highlights from that document: From April 2023 the general rule will be that the connection charges paid under distribution network connection offers will be decreased, as the extent to which the necessary reinforcement to the existing network is recovered from the relevant customer will be reduced as against the current position. For connections serving demand for electricity (or mixed use connection sites with import and export) in most cases no reinforcement costs will be charged to the connecting customer. These changes are designed to encourage a more dynamic and flexible energy system, in particular through the way in which distribution network operators manage reinforcement to the existing distribution network. The reforms may also benefit domestic households installing heat pumps and electric vehicle chargers as the charge for any wider distribution network reinforcement will be removed in most circumstances. Perhaps it will be worth me looking again at a larger PV system after next April. I hope it will also remove the charge we currently have to pay even to get an export upgrade even considered.

My guess would be the rubber that connects the drum to the front of the machine (someone will come along and tell us the correct name for it) has got a split near the top that only leaks when spinning, when water is getting splashed around a lot and it is at it's worst movement. That is only a guess. If it is, on some machines it is an absolute bitch of a thing to change.

If you are using an external control, you probably have to adjust a setting or even a switch in the ASHP to tell it to use the external input. Have you checked that has been done? Ideally you want two such extenal inputs, a call for heating and a call for hot water. My experience is few ASHP's offer 2. I had to get creative to effect such a thing with my LG heat pump. The reason for wanting 2 demand inputs is so heating and hot water can operate at different temperatures.

Post more details of your controls and how they connect to the ASHP

A few random thoughts meant to be constructive: With such thin sticks for the frame, and your proposed 100mm insulation are you planning a twin wall frame like a Larsen truss? Celotex may give a low U value for a given thickness, but is not really the best insulation, Earthwool or blown celulose in a cavity will give a much longer decrement delay, which in simple terms means it takes longer to heat up or cool down, but you will need thicker walls to get the same insulation. Under floor heating will allow the ASHP to run at a lower temperature and therefore a higher COP ASHP's operate heating the building or heating DHW not normally both together, this allows you to set a different flow temperature for each. That may not be the best choice of ASHP. Unless they tell you otherwise that one is not inverter driven so it will be on at full power or off and won't modulate down to match demand, and will likely have a large power surge at start up. you would be better spending a bit more for one that has inverter drive. It looks like a good project, look forward to seeing a floorplan and watching the project progress.

Why?

DIY on an absolute budget, I did not have luxuries like that. All mine went up the ladder. I estimated i climbed 3 Munro's up and down that ladder.

My plan would be 1) get planning for the new house. 2) Once you have that, speak the the neighbour about buying part of their back garden. You already have plannig so they don't have the leverage of you needing part of their garden. But if you can get part of their garden you can build the new house on a narrower plot and thus leave more of the plot with the original house. You could even arrange it with the purchase of a bit of the neighbours garden as the new house would be entirely built on your garden and the bit you were buying from the neighbour would just be the back garden of the new house and the new house would not be built on that.

Good news, that probably means the expansion vessel is built in. Do let us know what they change to fix it.

Why not? Elbow as close to the wall as you can get it, job done?

I sid mine the "old fashioned" way. Old dual rate electricity meter in line with the feed. (it was hard enough finding any dual rate meter for sale, this was the best I could get) The pilot wire is switched from the demand to the HW motorised valve, so the day rate reading on the meter is the electricity used when space heating, and the off peak reading is the electricity consumed when heating DHW

Expansion vessel has failed, usually the air bladder inside has ruptured. The pressure should not rise that high if the expansion vessel is working properly. Get it replaced ASAP, not something you want to ignore.

they come in different lengths, measure the distance from the face of the door to the centre of the hole which the square spindle goes through and buy the same length.

Those simple latches are cheap as chips. Never known one to fail like that.