@davesoa all very fair, I'm not questioning your plumber, just being cautious.

Just one warning about the UVC.  Heat pump cylinders have much larger coils than most normal DHW cylinders (vented or invented) -  3sq m vs 0.8 sq m. If you are having a UVC installed now then make sure it has the larger coil (which will make it physically slightly bigger for any given volume of stored water).  The coil size difference matters, and not just because of reheat time.  Currently there is no productized work around* (although one would be possible) so many installers will insist on ripping out a perfectly good UVC and replacing it with a new one if the original does not have a large enough coil.

(*exception - Mixergy do sell a work around for their own, rather special, cylinders.)

There is also an argument that a dhw tank for a hp should be larger to store more water at a lower temp.  This depends on usage though.

It's probably worth adding that many HP installers seem to insist you need 28 mm hw feeds to the UVC when fed by a hp.  This is usually BS, 22mm, the norm, is good for 6kW (arguably 9kW) under typical hp operating conditions, the equivalent of 2 standard immersion heaters.  So unless your reheat requirement is particularly fast, that should be enough.  This doesn't necessarily hold (although it may well do) however if your HP is larger than about 12kW.  Doubtless each installer will have their, often immovable, opinion notwithstanding the science.   Also many installers will want to use the hp manufacturers pre plumbed cylinder, it makes their job easier and means they can use rookie plumbers whilst still standing a reasonable chance of connecting it up properly.  In this case 28mm feeds are most probably required, depending on ho size, length of run etc.

The other one I've heard is that the CW to the DHW tank feed needs to be 22mm not 15mm.  Many UVC manufacturers 'recommend' this, but I can't fathom why it would be necessary if your mains pressure is reasonable.  This, however, is not a heat pump specific thing so your plumber will be able to answer the question for your house whether or not he knows about heat pumps.

Apologies if you already knew all or any of the above.

@davesoa all of those are good things to get done prior to changing the source to a heat pump, and I did a number of those things myself prior to doing exactly that.   In some cases actually myself (radiators) in other cases using a local plumber (for the UVC, as you need a specific qualification to do that, not DIY'able legally). The fact that your guy is asking about where does the "escape pipe" go suggests he is qualified. using your local plumber to do them may well be cheaper (based on labour rate) vs an "ASHP company".  And a local electrician for the sockets , same thing. 

even if you don't change the heat source it will make things more comfortable - with bigger rads you can run the boiler at a lower temperature, which "feels" nicer , and with an UVC (providing you have good mains water pressure) you can get better showers, and this all reduces what you have to ask an "ASHP" supplier/installer to do.

the only bummer you don't save the VAT. but that may be compensated by reduced labour rates. if you firm up on this with your local plumber please feel free to post specifics on here for review.

Thanks @JamesPa and @iancalderbank for those great suggestions. I’ll post back when my plumber and I have agreed what to do. 

@iancalderbank I agree.   Just bear in mind that the BUS requires MCS and MCS requires that the whole system has been designed and installed under the same contract.  My personal conclusion is that BUS costs me too much (because of the imposed restrictions) so I currently plan not to bother with this grant.

@jamespa I agree with you about BUS adding cost to install contracts. which is one reason why I did what I did. (see my write up).

But, if the householder has previously upgraded a bunch of radiators, and just so happens to have been forward looking enough to make them large enough that they would pass the MCS design criteria, then , as and when they want to go for a BUS/MCS heat pump install, there's nothing to worry about surely - their MCS installer isn't going to say "I didn't design those radiators so I'm going to replace them with some new ones that are the same size" ?

@iancalderbank "But, if the householder has previously upgraded a bunch of radiators, and just so happens to have been forward looking enough to make them large enough that they would pass the MCS design criteria, then , as and when they want to go for a BUS/MCS heat pump install, there's nothing to worry about surely - their MCS installer isn't going to say "I didn't design those radiators so I'm going to replace them with some new ones that are the same size" ?

Hopefully yes.  But if they fail to take into account insulation upgrades or extensions with a more modern construction, despite the fact that you tell them about them, then no.

I have had two full 2.5hr surveys done, one of which I paid for one of which was free.  In both cases their final calcs were based on solid walls throughout, despite the fact that I told them where the walls had internal insulation or were, in fact, made of lightweight block.  So in my experience the most likely answer is 'no'

@jamespa - off subject I know but how did you modify your post? I can't see a way to edit a post (though I'm sure there must be a way)

There is an edit button (see picture).  It disappears once someone else comments though

I’m pleased to say that the intended installer of my heat pump has fully refunded me. They kept me informed of the progress of the refund and we agreed the process which has taken less than two weeks so all credit to them (no pun intended). Not sure of my next steps though. 

@davesoa 

Sounds like a descent "installer".!

Unfortunately, I was threatened with a bill for £14000 covering the installation of a Samsung Heat Pump.

I was refused Scottish government payback "because my incompetent "installer" was STRUCK OFF by the NIC Regulator!

To protect me from an incompetent installer I was to be  landed with a £14 bill!

Fortunately the Scottish Government stepped in early December asking EST Scotland to repay the initial down-payment.

 Full marks to the Scottish Government and EST Scotland.......................no marks to the  MCS,NIC and RECC "Charitable Regulators".

YES!, your friendly Regulator , MCS,NIC and RECC , will , when on the defensive ,  reluctantly admit to being a Charity!

This "Charitable" status was imposed to provide "Light Touch Regulation" !!

ian

Horrendous is the only way I can describe my experience having a Daikin heat pump installed under the Eco4 grant. Forgive my ignorance on technicalities but I'm learning fast! It's 8 months on and I sit here with it all turned off as I await a Daikin installer to fix all the issues as it seems my installer hasn't got a clue and has just given up. They were here for 3 days last week correcting the miriad of problems still left by the Eco4 installer changing pipes and trying to sort wiring problems. Issues from the outset and when I had the funding inspection he failed the system. They had to move tank to loft and rewire something. Still issues, not least waking me at 3am 2 weeks later with horrendous noise in loft and another electrical issue and a leak into the floor where a radiator had to be moved. By then it was summer but it was clear some issues with the water. They sent the Daikin registered company out to check it all, but huge issues to be put right so back they came. Then summer over and no heat! At this point clearly installer had given up so I rang Daikin and handed over to the Daikin company again 2 weeks ago.  It's still not right and even they are baffled so awaiting someone from head office to come out, in the mean time left me with it running at huge cost trying to at least get me warm but had set it at 50c as the main set point but left me with no control over anything so not on room thermostat. Cost aside, which was frightening I was absolutely boiling and with days to wait for the return visit and someone from Daikin head office to come and sort wiring I looked up how to turn the main set point down (she had mentioned it over the phone) to 45 cost a bit less but still far too hot, turned it down to 40 next day and house way too hot still so lord knows what is going on. Still costing me way too much I tried the weather compensation curve but after several tweeks no heat and no clue what they have set it to I gave up and turned everything off 3 days ago as it was the weekend and no hope of the cavalry coming and the job they thought would take 2 days max has taken 2 weeks trying to find the issue. Frankly now scared it will never be right and I won't be able to afford to have any heat at all. 

@joti Oh Joti! This is very bad indeed. May I suggest you go into the settings on the MMI and set to LWT and set that down to say 35 (or a little lower if still roasting) you can set the slope to -3. Then set the lower limit to 25 (it probably won’t go lower than this anyway) and the right hand point to your intended room temperature (perhaps 20?). Now set the MMI controls for Weather Compensation and allow the system to do its’ reset and syncronise.  Have you a thermostat? That should improve matters until the cavalry return; you can refine it later. Regards, Toodles. (I have a Daikin EDLA0E3)