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Split if you’ve got a long (>20m) pipe run externally…. Personally I wouldn’t bother with the f-gas bod and would just get on with it, but then I’ve got the gear from doing r290 mini splits and r134 cars. Monobloc is better in that you don’t need to find room for any internal components (provided you don’t get a Samsung )

The other thing to be aware, if your heat pump only had a dhw valve live (or a heating valve live) output, instead of a separate switched live for each valve, you’ll need some relay voodoo to control the 2x 2 ports. luckily mine has both, but I ended up using a 3 port anyway because it was already on the cylinder.

Yep, I figured most people will be running with radiators, hence my statement…

Best controls (room stat will auto-adapt your weather comp curve for you, yes I know Mitsubishi also has auto adapt). Best backup if you’re an installer (vaillant take care of it all)

My vaillant pre-plumbed cylinder came with a Honeywell 3 port…. Go figure…

I’ve got the smallest vaillant cylinder, the 150 slimline (1m2 coil) being driven with a 9kW ashp - works perfectly… Glyn Hudson uses the same on a 5kW Samsung, again no issues. The vaillant cylinder is a decent one, coil is at the bottom for maximum efficiency.

125mm ish here…. No stat, fixed flow temp of 28… might turn it off next week, it has been on 24/7 since late October. Works perfectly.

Gas out, ashp in - house is warmer, larger and comfier for a little less per annum… And I don’t need to pay a gas-safe guy to mess with it, and we can get rid of the combustion appliance inside the house . Win-win… 1946 end of Terrace, on a hill, facing SW, 50mm cavity… it could cost Me £500 more per year and I wouldn’t care, it’s a superior way to heat a home. As for which one to install, one where the room controller/thermostat will adjust the weather comp curve for you instead of just turning the unit on/off. So Vaillant or Mitsubishi.

I know Tim well, I helped with the first stage steel column welding repairs (but wasn’t on camera, my mate David was)… He’s legit, his build is legit.

Brick/block makes more sense here…. Easily available materials, easily understood, easily tied into existing structure.

I use mlcp extensively, I’ll measure fittings bore for you this weekend. p.s. Unless you’ve got naff all water pressure, the reduction from the fittings won’t make any noticeable difference. your issue is 100% the incoming supply. Your plumber should have advised a new 25mm mlcp into the house.

Do that by rad sizing, not by zoning or trvs… heat pumps like direct, open, systems.

Same unit here, went in last September driving a mixture of rads, fan coils and a ufh mixer. DIYd the install myself. Works a treat, occupants happy. Might turn it off later this month, although we did have a frost again last night.

Yes, 3 port mid position valves are pure evil. However, Pretty much every single pre-plumbed heat pump cylinder from all the major suppliers use a 3 port diverter.

I’m not arguing you can’t do it, I’m arguing that no-one does (as it’s unnecessary imho). My Vaillant certainly doesn’t have it wired up thus…