JohnMo

Why unvented? Why a huge cylinder in the loft, when you have room for a plant room?

Wasn't talking gas price, was talking electric which is directly pegged to wholesale gas price, be wind or whatever.

The government ultimately set the rules

The biggest cost I have found with my self install is the piping, valves, armoured cable, and general stuff. But you are having to provide all that. I think the grant heat pumps come with flex hoses, so if all the water is within a metre no piping to install, no wiring - think they don't want the job and are pricing high.

We are being ripped off, all the energy companies are taking the p..., and the government is letting them. The pricing rules should be changed and only the government can do that. They don't care because the tax grab is great for them.

You really need to be dropping that another 10 degrees or more to get a good CoP. A 2 degree day and 50 flow temp is good for a CoP no better than 2.8. A flow temp of 35 deg on the same day is 3.8 CoP.

So the question is do you have to be a certified installer to install to MCS standards? Or can anyone follow the guidelines and complete a MCS standards install? You can install solar PV to the prescribed standard without being certified, so what's the difference?

Leaving aside the units being all messed up - if you need a 3kW or 6 kW ASHP at -2.5 you most likely end up with the same unit, once you start looking the actual performance at low temps, as not all manufactures rate their units the same, some will say the unit is 6kW, but at -7 only produces 3kW other will say 6kW but produce 6kW at -7.

Your not comparing apples with apples. Your daily usage is measured in kWh and is affected by the outside temperature, if it is warmer than -2.5 outside your heat losses will be lower - so less gas used. Your gas consumption also incudes DHW. The spreadsheet is calculating the heat power required on the coldest day -2.5, expressed in kW. So if the outside temp was at -2.5 for 24 hrs, you would require a heat input power of 5kW to keep a stable temp inside, so you would use 120kWh of energy that day

Your cylinder thermostat photo 2 is set high, it is likely your heat pump will struggle to get up to that temperature and will keep trying using loads of energy. Turn down to high 40s. Do you electric immersion in buffer and cylinder are these programmed to come on at any point. Call Grant heat pumps, they have specialist for ASHP that are supposed to help with commissioning issues etc. They hold the MCS certificate for most Grant installs. Get your quote out and heat loss usage estimate, this is a design documents and if you are using more kWh than specified, Grant maybe the ones who have to fix it, even with the original installer going out of business. Where is the controller installed? Inside or outside? How do you operate the system, are you running weather compensation? What are your typical flow temp for central heating? What is the thing with the blue lid?

If it's just the digging go to a ground contractor

Easy fix, shower, or don't spend ages in a bath

As standard install is up to 7kW and RED start at 10kW....not likely to be RED

Just go to SSE, they will do electric and gas. Electrical contractor just connects from meter installed by SSE to temporary consumer unit socket. Scottish water for your water, you need a temporary outside tap to their spec to connect to. If you want BT you need to contact them, they will not connect you until you need it, i.e. you start paying a standing order. But they will contact open reach and they will free issue the cable from house to pole.

Some heat pumps will let you run in full hybrid mode - i.e. both heat pump and boiler on together, other will not not so its one on or the other. Defrost cycle is not frost or freeze protection - very different, defrost cycle would never run with heat pump off line.. Freeze protection comes from freeze protection valves (opening the pressurised system to atmosphere to dump water) or antifreeze, the same as your your car (but a safe version of glycol).

My wife asked me to install a hot outside tap the other day. Added it to the other jobs on the list - another hole to put in to my wall

I recently went through the same thing. Also when I questioned the supplier about suitability for external use they said the C16 was not treated correctly anyway. In then the end anything suitable for external use was not in stock and had the be treated on request. So ended up with the specified C24 which was a 1 week lead time.

But is it down to building control, doesn't the mandatory installers certificate, trump building control?

There you go https://www.cylinders2go.co.uk/shop/uncategorised/telford-open-vented-300-litre-twin-coil-solar-and-heat-pump-stainless-steel-3-pockets/

50mm sounds small. My pipe going into the stove is aluminium. You can wrap in rockwool if you want. Rockwool doesn't burn

Mine was running for a few minutes while doing central heating, then being locked out for 10 minutes, this repeated over the day.

Not really, just use a 3 port diverter valve. My house started with a thermostat in each room, even with a big buffer ended with short cycling of the boiler. Basically have run this winter with no actuators on the manifold on weather compensation. Big saving on gas consumption 25-30% even though this winter has been much colder for us than last year. House temp pretty constant. Will be installing ASHP in the next month or so and intend to run just the same. But with a 3 port diverter diverting hot water to the cylinder as required.

Or you just drive the pump from the thermostat switch. I would use the manufacturer controller every time. Set it to weather compensation, balance loop flows. No thermostat other than the valiant control. Operate as a single zone. If you have a towel rad stick an electric element in it, to make it dual fuel. Good for summer towel drying. Also gives you two zones to comply with building regs

Could use a phenolic insulation boards like Kingspan Kooltherm K103 Floorboard. About 10 to 15% better than normal PIR, but quite a bit more expensive. Or normal PIR boards. Put it down in two layers with staggered joints, all a tight fit. Fill all gaps with expanding foam and tape the top layer. Thin polythene sheet, staple the UFH pipe to insulation through poly sheet and then screed.

No you don't need to make it each room a zone as you seem to be stating. If the property is over 150m2 you need two zones. No more than that.