JamesPa

If, by the last sentence, you mean force everyone who has a heat pump to have a new cylinder, I refer to my previous comment. If you mean something else then please lets discuss solutions not kid ourselves that the problem doesn't exist. Gas boiler replacements cost 4-5K and dont involve the disruption of replacing the cylinder. Thus it follows that replacement of a heat pump with a gas boiler must also cost about the same otherwise its not going to happen. Think of this from the perspective of a low to middle income householder, or a penny pinching landlord, not from the perspective of a self builder, an installer or the HPO industry. 1.4M of them each year replace their heat source (gas boiler) in most cases because the exsiting gas boiler has failed or is uneconomic to repair. They don't expect to replace their DHW system at the same time. How can price parity (or near parity) possibly be achieved if you insist on 2-4K worth of unnecessary DHW system replacement (and associated disruption) in addition to replacing the heat source. It cant, so we have to find a way to accept alternatives otherwise the roll out of heat pumps is forever crippled. Some of the suggestions you make for regulatory reform are spot on, but some rely on market distortion of a nature which costs poor/poorly educated people money. This plays directly into the hands of the right wing extremists who are already ruthlessly exploiting climate change to their benefit, so must be used with caution. Climate change already plays into the hands of the facists/right wing extreme, we simply cannot afford for the Heat pump industry to make it worse. So lets get real, we need two things at pace to address what are surely the two majority use cases for HP retrofits to substitute for the 1.4M gas boiler retrofits which take place each year: 1. A way to replace a gas boiler coupled to a DHW tank with a heat pump, that costs (without government subsidy) about the same as a gas boiler replacement alone. I submit that this rules out replacing the DHW tank in most if not many cases We appear to have this technologically with modern R290 (or even R32) pumps. We also, as you say, have a solution with pure electric provided the heating is done at cheap rate. But currently neither are deployable, the first because the industry wont do it apparently and the second because of the silly rules which say that grants are available only for 100% space + DHW heat pump solutions. Something needs to change so that ideally both of these solutions become deployable. 2. As above for the case where there is no existing DHW tank. We don't appear to have this so, at present, I cant see this yet as a mass market. Something needs to be invented/change to fix this one.

If that's the case, and I fear you are right, we can forget any prospect of heat pumps being installed in the quantity we need to deal with climate change without continued government subsidy, which won't happen. Curtains for heat pumps and humanity. The gas boiler lobby has won, thanks to the heat pump industry. Seriously. If anyone can see a route to heat pump installs which is both financially viable (for the average person not the privileged few) and viable in terms of disruption, but where you nevertheless rip out a perfectly functional DHW system, please come forward!

Of course, but there is nothing to stop Vaillant from indemnifying the installer against claims.

Given all of which is there any realistic chance of persuading Vaillant or a Vaillant specs installer to reuse an existing cylinder with a typical 0.7 sq m coil or is it a lost cause notwithstanding the devastating consequences of the wholly unavoidable continued use of fossil fuels they are effectively encouraging.

Which is very logical, however @sharpenerstates upthread that Vaillant take responsibility for the system design if a registered installer is used.

Vaillant do. In addition they have a field engineer force who will come and troubleshoot installations done in line with HQ approved designs, whether generic or custom. You can also call them out to fine-tune your system e.g. after the first year, said to be well worth the £300 or so. Or so I glean from e.g. the facebook group. Thanks to @DanDee for posting the link. There seems to be some ambiguity over who takes responsibility - see the text which appears above the schematics. I think the key question remains: Are their registered installers actually prevented (by threat of guarantee withdrawal) from departing from hq guidelines/rules of thumb or whatever they call them, or are they free to depart if they choose to, with Vaillant withdrawing only the relevant parts of any guarantee? The latter it seems to me is entirely fair, the former not so.

The key to innovation and flexibility is surely is the second part of this sentence, which Vaillant appear to prevent based on what you say. Are their registered installers actually prevented (by threat of guarantee withdrawal) from departing from hq guidelines/rules of thumb or whatever they call them, or are they free to depart if they choose to, with Vaillant withdrawing only the relevant parts of any guarantee? You mentioned you had the book of approved system designs, any chance of a link please?

It's essentially heat_loss/deltaT * degreedays * 24 Heat loss in kW and answer in kWh. Where deltaT=design temp of room minus outdoor temp (about 22 in the south east UK) and degreedays is the number of degreedays per year in the location (about 2000 in the UK). 24 is of course the number of hours in a day. I'm not sure if MCS do any tweaks but that is the basic formula.

The more I think about this the more it exemplifies a structural problem. We simply don't, in this part of industry, properly differentiate between component design/specification and system design/specification. Vaillant, Mitsubishi etc are making one or more components of a heating system. They don't attempt to make them all, and they don't attempt to ensure that all the cases where their components are used meet the customer spec. So what they need to do is provide as much info as possible on their component, guarantee that for as long as they see fit however it's used (so long as the interfaces to their component aren't violated), and butt out of everything else. They can of course provide application examples, but these are examples only not constraining. The system designer then needs to take the specs of the various components available and assemble them into a system that meets the customer spec. The component supplier warrants the components as long as the interface conditions aren't violated. The system designer warrants the system. This is well established in eg electronics, and if component designers in electronics interfered in system design in the way you describe Vaillant as doing (but without actually taking responsibility) electronic systems would not have progressed anything like as quickly as they have. Of course one problem is that we don't really have domestic central heating system designers, we have plumbers. They can solder together the electronic components but aren't trained, in most cases, to work out which order to solder them together in. So the component designer (vaillant) tries to step in, but in doing so makes any system design sub optimal, particularly in a retrofit situation where certain things are already in place. Imagine if Intel, rather than sticking to making comprehensively specified microprocessors, tried half heartedly to provide guidelines on their use and restricted their warranty to people who referred back to them for every departure from those guidelines. Would we have the diversity of microprocessor based systems we have today? In an ideal world the heating system design industry would step up, and the heating component manufacturing industry would provide comprehensive interface and performance specifications and otherwise butt out. Will this happen? Probably not, because the boiler/hp manufacturers regard themselves as the heart of the system (no more so in fact that a microprocessor is) and we don't, for the most part, have a system design industry, we have a bunch of artisanal fitters (there are of course exceptions). For anyone with an engineering background or skill, or anyone that wants to do something even slightly out of the ordinary, that is massively frustrating. The average person, however, is probably oblivious both to the lost opportunity and the extra cost.

That begs more questions than it answers, no fault of yours, the fault of vaillant. Eg Are the as restrictive with gas boilers? Who is taking responsibility for the system design, installer or Vaillant? A 'rule of thumb' is not a design, will they give a more specific answer to a vaillant installer or will they give an equally vague answer which gives them a get out but doesn't protect you or the installer in any way? Is the whole thing just a way to make their 7 year guarantee in practice 'at their option'? Having regard to the above is their 7 year guarantee worth the paper it's printed on? Do they actually want to sell heat pumps, or do they prefer to sell boilers? and several other questions.

Comes down to a)Price b)Whether you either know someone who can do the system design/install outside MCS or are prepared to learn enough to do it yourself. If b) is true then you will quite likely get as good or better job than many (but not all) MCS installations at a similar or lower cost even without the grant. If b) is not true I'm not sure you have a choice. Doing it outside MCS requires express planning consent (which you appear to have) and excludes you from the grant. On the plus side you don't have to pay the MCS fees (which are bundled into the MCS installers price) and you aren't bound by rigid MCS rules which don't always allow the optimum design choices. MCS will argue that MCS gives you better consumer protection, others have a different opinion.

Yes but that will always be the case with installers. At least with no constraints from Vaillant they can't hide behind an immovable third party.

Absolutely perfect, it says nothing so imposes no silly constraints.

Daikin, for some reason do. But I agree with your logic and it's better if manufacturers don't because then there is no poorly thought through backside covering spec for MCS to insist you follow.

Don't see how they can do this unless it's built into one of the conditions. Building control sign off is of course necessary, but that needs only to meet the BC rules

Definitely possible in principle but might require an installer who can think out of the box and violates the requirement for a grant that the hp must provide 100pc of the heat load. There are some out of the box thinking installers, but they are few and far between.

Another reason to defer a dhw upgrade if you can. There is the distinct possibility of some more intelligent technology in the next few years. So if you have a perfectly functioning tank which is say 10 years old, why swap it out now for a UVC where a lot of internal space is taken up by a coil which you can't service and which introduces a load of G3 hassle, when something better (even if it's only a tank with an external PHE) is likely to come along before your perfectly functioning cylinder meets it's maker? PS a not such a joke sunamp would be attractive to me for my own house, it's not just landlords who might want one. But as you say at present not up to par.

I'm not sure anyone is blaming installers for including dhw heating, its clear that the grant requires it. The discussion is whether this has to be done by replacing the cylinder. I reckon that most of the actual install risk is in this not in the heat pump itself. An installer has no idea what he will find under the floorboards (assuming he can get under the floorboards) when he tries to fit the UVC vent pipe with a continuous fall, new feeds if he insists on them and replumb bits of both the cold and hot water to suit. So while fitting a heat pump is like fitting a boiler, fitting a heat pump plus UVC is a whole different ball game. I can see why installers allow one week x 2 men, so do 1 per week. The hp only job is much more straightforward and I would reckon that 2 per week is easily achievable. Not necessarily less lucrative and an easier sell. Obviously a bit of prequal is needed, but if the gas boiler gets the water to temperature then a hp running at 70 will do also, unless it has a really poor modulation ratio in which case the installer shouldn't be selling it anyway (or the house genuinely needs a 16kW heat pump which is rare).

The thought of a UVC in a rental property gives me the screaming heebie jeebies. The tenants will only report something wrong when leaking water has done major damage or if there is an actual explosion. Avoid in my book. Probably this is an excellent argument for heat pumps as opposed to boilers in rental properties. Gas can explode, properly installed electrics are pretty much idiot proof.

Do Vaillant actually specify any requirements for a third party dhw cylinder. I couldn't find anything in their installers guide. A rule of thumb isn't a specification and can be ignored.

Fair enough. I will drop mentioning this unless I can find proof of requirement somewhere. Having said that the average householder might not be 'competent', so as a general point in relation to how not to sell ashps the point arguably still stands.

Really? So I can buy this with a 10kW, or even a 7kW, Vaillant heat pump and violate their rule of thumb? Or is it just that they are happy as long as you buy Vaillant?

Interesting. That's a 'rule of thumb' not a specification. The MCS requirement is that you must meet manufacturers specifications not their 'rules of thumb'. As you say a woeful misunderstanding of their own product. I feel a trawl through their installer guide coming on.

+1 on this analysis. Plus the annual cost of a G3 service (which wipes out the cost saving on energy) + given (iv) it's surely likely that a more elegant solution will appear in the next few years (eg a bolt in phe/pump).

Fair enough, but my point is that the decision, on that basis, is one for the customer not for the installer or the industry. The installer needs to tell the customer the facts that they know and let the customer decide based on those facts and the facts only thee customer knows. Also the dhw upgrade can still be done later if the customer changes their mind, with nothing lost. Or done a different way if PHEs take off in the hp world, which seems at least plausible if not likely.