ProDave

It seems common that mass market house builders have a reputation for poor service. Get a bucket stood up in the loft to catch the drips for now to save the water soaking into the insulation and wetting the ceiling, you might need a board or a plank to stand the bucket on.

That picture looks to be rotated, i.e. south up, unless you are in the southern hemisphere. How about a ground mounted PV system at the southern end of your garden? Then make it into a shed:

When measuring a building, e.g. a shed, they count the eaves height as the height at the lowest point. Personally I would just do it, you don't want to have to put a step to keep it under 300mm do you?

That looks like it was concrete, and the passing travellers put a very thin coat of tar on with no preparation and it has predictable failed. As above get it done properly next time.

Get the installer back and pose this question to them. Or check with for example an IR thermometer what the actual flow and return pipe temperatures are at the heat pump. Is there a buffer tank in this system?

So it's a 10kW heat pump then. Probably half the power of the previous oil boiler (that struggled to heat the original house) so lets hope the now enlarged house really has some better insulation. you NEED to pester the builder to find what calculations they did about the expected heat loss of the enlarged and hopefully improved house now, AND find out exactly what insulation has been placed under the UFH pipes. Assuming the enlarged, but better insulated house still needs the same amount of heat, then 14890kWh of heat delivered by a heat pump at a COP of 3 and a present electricity price of 20p per kWh will cost £992 pa

So you had an oil boiler that struggled to keep the house warm. You have replaced it with a heat pump that is probably lower power than the previous boiler (I have failed to find what output power this heat pump is, Daikin don't make it easy to find out) and still have the problem that downstairs does not heat up enough. You are relying on the improvements to insulation to even make the new lower powered heat source work for your house, but don't seem to know much about the insulation fitted. You talk of 40mm floor insulation, if that is all you have it is WAY too little for under floor heating. Did you pay for all the upgrades to insulation and the heat pump install as a package to one company? If so I would be getting them back to sort it out. If you are struggling with an outside temperature of 8 degrees, you are really going to struggle when it gets properly cold. To give us some idea of expectations, how much oil did you burn in a year with the previous boiler? That will give an idea of the heat losses of the house prior to any improvements. Unless they fitted a dedicated electricity meter for the heat pump, or your has it's own metering built in, it is hard to actually measure how much it is using. In our house the heating is only about a quarter of all electricity usage.

So you are just guessing. Make and model of ASHP? Type size and age of house? insulation levels etc? Has this just been fitted? what if anything was there before? Was any SAP or other analysis done predicting heat load requirements?

What heat pump do you have that has a fixation about delta t? My own (LG) heat pump just sets "Leaving Water Temperature" i,e, the temperature of the flow leaving the heat pump. It does not care about the return temperature, it just adjusts it's power output to keep the leaving temperature at the set point. When only 1 UFH zone is active the return temperature can be very close to flow temperature and the heat pump will run at very low power. Exactly how are you measuring that the heat pump is consuming a lot of power when delta t is very low? that does not make sense.

5kW monoblock ASHP driving wet under floor heating and a 300 litre unvented hot water tank. 3 bedroom 150 square metre 1 1/2 storey house. Well insulated and air tight to near passive house levels, calculated (and borne out with actual figures) worst case heat loss about 2.5kW I do have a room sealed wood burning stove as well. It will heat the whole house, or rather it MUST heat the whole house, shut the doors so the heat is confined to 1 room and that will very quickly overheat, it only works because the house layout allows the heat to travel to all rooms. It supliments the heating to use up free wood and reduce electricity usage, and as a backup in case of power cuts. And for those grey wet days when 20 degrees feels "cold" when it is dreary so we use it to crank things up a bit.

We are just north of Inverness in a frost pocket (when the news says frost in sheltered glens, that is us) and the ASHP has no problem. Once it gets below 0 there is little moisture in the air to cause it to frost up, and it regularly works at -10. the worst temperature fro frosting is just above 0 when it's damp and lots of moisture in the air.

No 1 big thermal store that provides both the heating and hot water, and that same tank can be topped up using an immersion heater and surplus solar PV. You need something like this because a stove generates a lot of power and is "unctontrolable" so needs plenty of capacity to absorb it's heat output. Being a large tank means the stove only needs lighting perhaps once a day or even less.

This system works best with a stove heating a large thermal store which will supply hot water and run the under floor heating. With the solar PV, install a diverter to send excess PV to an immersion heater. Unless you have a LOT of PV you will probably find batteries unnecessary.

We have one but never used it for the build. Timber frame so not much wet trades other than plaster skim, done in the summer, lots of windows open to dry it out quickly. We bought it when we had a previous 1930's house that was always damp, due to poor build methods of the time and no insulation.

Being pedantic, no they don't. They just have to be listed in the same order as they are physically presented. I had a few out of date order and had no complaints.

The water that passes through the ASHP will be a sealed heating circuit with inhibitor added so I don't see it as a problem. Your hot water tank will be prone to scale but that is not what you are asking about.

I read it as 4 strings. So you will need to take each string individually to the inverter via a DC isolator switch. So that will be 4 lengths of red and 4 lengths of black cable. So each string is 7 panels, and you have 4 of them, that's likely to be an 8kWp system

Be VERY careful, that voltage will kill you and what's worse it will bloody well hurt all the time you are dying. You normally leave at least one panel unplugged so the string is not completed until you have done ALL the DC wiring. Go and unplug one panel off each string before you do any more. As above 4mm or 6mm cable will be fine, make sure what you buy is sold as DC solar PV cable with a voltage rating of at least 1000V it is available in red and black colours.

Even my as built SAP over estimated my heating energy by about 3 times. It had all the correct information about the building structure, windows, heating system, actual air test etc. I found Jeremy's simple heat loss spread sheet a far more accurate heat loss calculator than the SAP. I often ponder how much better the SAP rating would be if you could somehow input real life measured heat input rather than the theoretical figure it calculated.

Didn't he build and finish the second house just so he could borrow against it's value to finance the big house?

Astra 2 28.2E for Freesat and Sky.

I take it this is not ground floor? I have found many old traditional cottages here with what looks like clinker in the inter floor void. Was that there for insulation or sound deadening?

Yes perfectly allowable, except the SVP you run up the wall must go above the roof line, you can get black white or grey pipe, the orange is only for underground. And then it is the internal pipes that terminate in an air admittance valve at the top of each one.

I am not surprised because HE does not want to be blamed for polluting the land drain and the pond with sh1t.

An update, not really because there is anything particular new to report, but more of a diary. I had the heavy wind driven rain followed by sharp frost that provoked the start of this thread. Not long after my last post we had another sharp frost, and no blistering issue. And since then we have had a lot of cold weather including right now, where it has been well below 0 for several days, the whole north facing side of the house is covered in a glistening layer of frost and not blister, bulge or any issue to be seen anywhere. This reinforces my view that the problem occurs when we get heavy wind driven rain that allows some moisture to get through the top coat, that then freezes, expands and blisters, possibly cracking the top coat in the process making it easier for more water ingress. The fact it does not blister again when it freezes a week later, suggests whatever moisture has got in dries out fairly quickly. And the fact that now even after a lot of sub zero weather, there are no other signs of problems suggests there is no other underlying moisture issue apart from the occasional heavy wind driven rain, which is a bit of a relief. So now it's a case of wait and monitor what happens to see if there are any other issues that need remedial work or not. Still fuming that Baumit are not interested in even looking at the problem or giving any advice.