Just curious, is this a new build, a BUS install or something else?

The hot water cylinder had a started to weep around the immersion port and the immersion was well stuck, so I replaced the cylinder with the Viessmann 200l heatpump cylinder... it was basically the only one with a diameter small enough to squeeze into the airing cupboard without going with the slimline versions which are way taller for the same volume.

So with a cylinder suitable for a heatpump, I decided to rip out the storage heaters and install extra radiators in their place and seperate the older hydronic system from the stove.

Being as I'd decided on a DIY install, I didn't see the point in paying for a premium brand, because I wouldn't be covered by the extended warranty. Graham has several videos on his YouTube channel and the overall quality of the Haier units looked to be a reasonable option. After looking through previous electric readings from the smart meter, I settled on the 6kw model which meets the usage plus a margin. I did heat loss calcs to size the new K3 radiators; except for a towel rail which ive replaced, the existing radiators were all OK.

I've used pressfit fittings almost everywhere because the elbows have a nice swept bend compared with the much cheaper end feed or Yorkshire solder fittings. But I've tried to bend the 15mm and 22mm pipe wherever possible, rather than using fittings. Ends of the pipes have been thoroughly deburred to prevent undue restrictions.

If I was doing this again, I'd certainly be looking into a coil of 32mm MLCP instead of lengths of 28mm copper as the reduction in fittings would easily cover the cost of some new jaws. I'm sure it would have been easier/quicker and cheaper overall.

Posted by: @singlespeed

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Being as I'd decided on a DIY install

Very nice! Congratulations.

Posted by: @singlespeed

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32mm MLCP

Big MLC looks neat when it's finished, but it is quite uncooperative... gives a good full body workout 🤣 

Posted by: @bobflux

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gives a good full body workout  

All the 45° elbows required for getting the primaries into a lower loft space, then up into the main loft to connect with the old primaries and HW cylinder was a mental workout and rather awkward

I could have avoided that by going up the outside of the house and drilling through the gable end into the main loft. But the wall is around 18" thick solid stone and there's some quartz and granite blocks lurking under the render 😬

It's alive 😀

I actually got it switched on yesterday, but I was going around in circles until I realised that the diverter valve must be the wrong orientation. I'd also need to re-read how to enable and set up weather compensation. So I switched it off and rotated the diverter this morning and set up the weather comp and schedules for heating the DHW during the cheap rate.

Fantastic. 

I am wondering how the support from Haier has been? And how widespread is their network of heatpump service engineers - unless you are planning to also go DIY? 

Theres comprehensive instalation and service manuals (IM, SM) available on their Website, as well as all the specifications in the engineering data book (EDB).  The build it yourself book is an abridged guide of the installation manual and helped to get me running.

The one time that I contacted support, was to get the detailed outputs for the units, because I couldn't find them. They replied within the hour with the information (pages from the EDB)

Apart from sealing the external Primary Pro joints and fitting another meter of insulation to one of the primaries in the loft, I'm finished.

I

Having flushed the system and finally connected up the last secondary branch with no leaks apparent after bleeding and the pump running for an hour, it was straight forward to add inhibitor into the top of the towel rail. Shut off both inlet and outlets. Open drain valve and then open bleed valve to let some air in. Drain off two and a bit litres and close the drain valve. Remove the bleed valve fitting and add the inhibitor. Refit the bleed valve fitting and re-open the inlet and return. Bleed off the air and tidy up.

As well the outside air temp getting down to 3° yesterday morning, flushing the system with cold water and also having to loft hatches open, probably accounts for yesterdays higher readings. Plus there's the three additional radiators connected. 

My actual electricity usage isn't really any different to what it was prior to switching over to the heat pump! However it was only the living room which was heated to 20° in the afternoon and evening. Now the living room is 20° all the time, along with the bathroom and WC. Kitchen hallway and spare bedroom are all 19°.

It's rather underwhelming, because it's just nice and comfortable.