JohnMo

They do. Min size should be, based on number of beds would be 270L. Section 3.5, would say 175 and 210L are way too small for a 5 bed. https://mcscertified.com/wp-content/uploads/2025/02/MIS-3005-D-2025-V1.0.pdf

Not the best decision, but yours to make, as long as the size of cylinder complies with MCS regs - which it may not unless your in a 2 bed property - your worst case is short cycling doing DHW. Plate load as a minimum, ideal skip it and a suitable sized heat pump cylinder.

My comments 22mm main run for DHW, will take an utter age to get hot water out the tap. You really want a manifold system. Mine is DHW cylinder - 15mm to manifold central location, then from manifold 15mm run to each wet room and spur from there. No comment on price

Going to be less than efficient doing DHW, via a heat pump, as you will have higher flow temperature to get the same cylinder temperature. It also sounds a very small cylinder for the high usage of water you seem to have. There are only two of us and we have 210L and wouldn't want any smaller.

So is your existing cylinder a typical gas cylinder? Or a direct cylinder (just immersion)?

Where are you located - your profile dies show it? Your design case (outside temp) is something like to cover 99.7% of the time, so your -8 is very likely not going to be applied. Why, do you have a heat pump coil or are they adding an external plate heat exchanger?

Still no idea what you are doing - over thinking or a real design issue, is it 1 m² or 100m², ground floor, 1st floor, what is the steel doing?

Take some stuff through the wall?

Observations the untrimmed room temperature is higher than that used for trimmed, TRV and smart trv, so no surprise you use less energy by lowering the room. Your CoP will remain similar as you have the same flow temperature. Achieving a reduced house temp via running a second set point would have resulted in an increased CoP and further reduced energy consumption - due to lower flow temperature. So why not add use native controller for the heat pump to manage setbacks, if you need them. Or just get house to sit at a stable lower temperature and take a win for simplicity, less cost upfront.

Only thing you have to watch is actual engagement water capacity with a heat pump or boiler. To prevent short cycling you need to maintain 20L of system capacity per min output kW - any radiator or UFH circuit operated by a TRV or thermostat is basically excluded from the capacity calculation. Plus you need to ensure minimum flow rate is maintained in all operating modes. If you are not careful this can drive a buffer or volumiser. A buffer will add costs for vessel and additional pump, it can lead to flow temperature distortion and reduced CoP. A volumiser adds cost during install.

First heat pump name plate ratings are meaningless. They all take a different datum point for the rating. Vaillant tend to use a low ambient. Worst thing you can do for efficiency is oversize you heat oump. On the design day and they don't happen often you can always flick on the immersion, but doubt you will need too.

Not sure how you have worked that out? Think you need to explain in more detail what you are trying to do. I have thick tiles on a stud wall and plasterboard - no steel in sight. So confused what you are or aren't doing

Why bother with lightweight?

I did, put some smart stuff in, but was way more work than it needed to be, so now have a box of smart relays gathering dust. Good old light switches and 5A sockets for side lights. Works every time. Not sure I need lights changing colours or themes and then the wife nagging me why can't we just have stuff that works. KISS.

Check for moisture. If present use a liquid dpm, which is an epoxy type paint. Use a self leveling compound as needed to get level prior to Dpm paint. Bond floor direct to dpm. Why do you need to screed? Herringbone, lifes too short, for the faff and living with it if you don't get it perfect. Keep it simple.

Have you submitted your completion certificate?

I would leave bathrooms where they are, keeping living and bedrooms as separate areas. Moving a bathroom sound lots of work for little gain or loss of convenience. Then form a kitchen/diner, robbing some space for utility

It does sound a huge heat pump based on a new build even to min building regs.

If your putting a battery to cover your whole winter loads, it going to be huge and not cheap. I would size it now for an average winter day. But your tariff makes a big difference to the size, Cosy gives you 3 charge periods, a typical electric car tariff only one, so you would need a much bigger battery. Just choose a battery that can be expanded, add more later if you want as slave units.

Not so good. But it prompted me to do an exercise on my non Hep2O manifolds valves (after 5 years). Sorry can't help answer the question. But have you tried a socket or ring spanner?

Listened to podcast on electricity pricing and its way more bonkers than that. Can't recall the exact pricing mechanism, but its a bidding system. I could bid to supply electric to London although I'm in NE Scotland, be within the pricing range deemed acceptable, they would then look and say its not practical for me supply that electric to London as I am too far away, and then pay me not to generate and instead pay another supplier the highest bid to supply the electric. Until the system is simplified we are stuffed. Plus there are so many cost adders to the price we pay, it always going to expensive. Generally the policy setters and the wholesale pricing system has completely lost the plot

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I'm running 3 inverters. 1kW, 3kW and 3.6kW. I take 3.6kW and 1.0kW in to a small consumer unit with C Curve Type A Double Pole Compact RCBO (Bi-Directional) as they feed down the same cable to the house. None of the inverter talk to each other - its crude but no issues. Over clocking the inverter is easy enough. The 3.6kW has 5.8kW of panels connected to it (within voltage limits). I just accept that at around midday a whole chunk of electric could be clipped off. I have over clocked for winter performance, not summer in summer I generate a tonne anyway. The 3kW has export control and can switch the whole array off if the battery is full and I am at my export limits. Our voltage today has been about 245V at some points I was generating 6.5kW.

I was over run with vermin, used bait stations, first year got though loads of bait, now bearly any.

Think you either have to expect the following 1. MCS uplift in prices for everything then a vat reduction - overall expensive cost. 2. Buy it all yourself, pay the vat, either install yourself or get your local electrical guy to do it. Lower cost overall. I would leave original install untouched. Do the battery AC coupled then it's a stand alone job no scary PV involved for you electrician.