@matban , I have a couple of thoughts. 1) consumer protection act 2015, fitness for purpose. 2) You appear to be saying you have  heat loss of 5kw, so if you get an 8kw, so over the top, BUT as it’s the 4,6,8 kw unit, the lowest output is the same.

3) When you bought your house and contents insurance did you include legal cover? If you did I think it’s worth a chat with your insurance company.

My belief is that octopus should not be charging you for rectifying their errors. Errors that include incorrect heat loss calcs. Poor quality install. In fact they should be replacing at no cost AND compensating you.

But I have similar issues with BG and have been through the whole complaint process to no avail. So this winter I am logging everything in detail and if they don’t address the issue, I’m going the consumer protection act route thru my insurers.

Best wishes. 

Posted by: @terry1812

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2) You appear to be saying you have  heat loss of 5kw, so if you get an 8kw, so over the top, BUT as it’s the 4,6,8 kw unit, the lowest output is the same.

Yes but 9kW is similarly the 16kW derated.  So 8kW substantially better.

Posted by: @matban

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What should I do?  It seems I need to take on Octopus and the industry to get them to pay for the rectification entirely.  I can afford the 2k and it is quite tempting to get this resolved with out a big continuing fight throughout the winter whilst being regularly woken up at 6am.

You will face an uphill battle for sure.  I think it depends on you. 

You could certainly push Octopus further threatening action under the consumer protection act.  If it does in fact heat the house (which is the primary purpose if a heat pump) you will need a solid ground to claim unfit for purpose, either materially less efficient than is reasonably achievable (violates building regs) or unreasonably noisy.  Do you think you have that and if not could you make the case. 

If you can't then perhaps you are better off negotiating a bit more to ensure you have achieved the best consensual outcome and then settling.  You never know you might get a much better offer if you just ask forcibly.

@terry1812 Thank you for your reply.  Yes a 6 would probably be fine.  I haven't checked the actual output vs temp chart for it.  But with the 6 and 8 having the same hardware and minimum modulation there doesn't seem to be any reason for the 6.  Perhaps the control algorithm is less aggressive but that is just a guess, I haven't seen anyone say that they behave differently.  A little hard for anyone to know other than Daikin.  

I'm sorry to hear you are having similar issues with BG.

@jamespa thank you for your thoughts.  It does seem to be a choice between a long battle with an uncertain outcome vs a financial hit but with a much more certain and timely outcome.  The negotiation idea is good one, nothing to lose there.  If they would go half way I would feel much better about the whole thing.  I do feel some sympathy for them in that the default ACH figures are highly misleading.  The regulations are ambiguous. If you read them from the perspective of getting a really accurate heat loss calculation then your interpretation might be that measuring ACH was essential.  If you read them from a perspective of how to get a good enough and compliant calc for the average house then you might interpret that default ACH is fine.  Without real world experience of how much ACH actually varies and the percentage of error it introduces to the calculation the latter is the more likely interpretation.  I don't think that this should be put back on me though, Octopus should fight for clearer regulation, they are in a considerably better position for that than I am.

It's increasingly clear that there is frequently problem with heat loss estimates and ach is one of the culprits.  There are some installers, including a few here, who will acknowledge that but most won't so far as I can tell and just stick to the safe (for them) MCS rules.  I was fortunate to find one who would assume ach 0.75 for my 1930s house and use my gas consumption as justification.  Few would do this though even though the evidence was clear.

It costs about 300 I believe to do an ach measurement and it can make a big difference. Doing it every time might be going too far however.  Personally I think installers should be obliged, wherever possible to run a sense check of calculated loss vs gas consumption or some other independent measure, and if the two don't correlate suffiently well, to reconcile, if necessary by doing further measurements including ach if appropriate.  Unless and until this becomes the norm, cases like yours will continue to occur.

If you do decide to negotiate I wish you luck.  Even if you don't get any further concessions you will at least have the comfort of knowing you tried.

@jamespa The problem in taking the gas figure is that everyone consumes differently. I had a similar issue about my EPC. But as the surveyor correctly pointed out to me the survey isn’t for you it’s for the house. That’s why they use the average figures. If people had used my gas as a means of assessing my heatloss it would have been way too low. I’m also thinking that the heatloss arising from the ACH is usually a very small amount in comparison to the overall figure.

Posted by: @terry1812

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I’m also thinking that the heatloss arising from the ACH is usually a very small amount in comparison to the overall figure.

Not so.  In my case it made the difference between 10.5 kW and 7kW.  There are a fair number of others who report similar eg op on this thread.

In any case a sense check doesn't just concern ach, it takes in every opportunity for the survey to be wildly out.  For surveys to be out  by a factor of 2 (as mine were) appears not to be uncommon and makes a vast difference to a 6kW house!

Posted by: @terry1812

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The problem in taking the gas figure is that everyone consumes differently.

Yes but (a) this makes less difference than you might first think and (b) it can be factored in to an extent with a questionnaire, or almost completely if you have half hourly readings, which many will.

The plain fact is that the current system results sometimes in errors of a factor if 2 or more.  It makes absolutely no sense not to sense check it against a measurement if you can, which will be possible for the vast majority of retrofits.

If the two correlate reasonably then proceed, if they don't then find out why before installing the wrong heat pump and ripping up floors unnecessarily to upgrade pipework.  

The current system benefits the industry by providing an ironclad get out for installers at the expense of the customer.  That is immoral.

@terry1812 James is correct, the ACH are often the largest factor and can change the heat loss by a 1/3.

We design often based on 1, it takes experience to look at a 40yr old building and see they have had improvements made over the years and now the standard air losses do not apply.  

@matban If you have to concede and I am not saying you should but for less fuss if thats what you would like? If you do, reverse the offer, tell them swap the ASHP for a 6 or 8 at their costs and you will offer to pay the labour for their time which would cost 1/2 a day to change that part only, this would cost you around £350.00 may be a bit more. all of the rest of the issues should come under warranty. This way you get a new correct sized heat pump which should run at a better efficiency so I am thinking you further gets some saving back and hopefully resolve all of the other issues.

If you think you can hold out and they have not done the correct design, job and commissioning then do so as long as you can bare it and perhaps they will show goodwill. I would imagine with their buying power that they sell so many Daikin's that they could get one for free from the supplier anyways.

I wonder if any of the employees are on the forums here? 

Unfortunately we are a company that complete a lot of Retro-fixes "coined name by Mars" but I am not so great in helping how to get their money back as I am not a consumer expert and TBH if our company completed an install to what you described I think I would give them a whole new system or a big chunk of the money back. 

Posted by: @terry1812

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@jamespa The problem in taking the gas figure is that everyone consumes differently. I had a similar issue about my EPC. But as the surveyor correctly pointed out to me the survey isn’t for you it’s for the house. That’s why they use the average figures. If people had used my gas as a means of assessing my heatloss it would have been way too low. I’m also thinking that the heatloss arising from the ACH is usually a very small amount in comparison to the overall figure.

The ACH can actually make a huge difference.  My heat loss is 5kW in reality and with the correct measured ACH and more than 7.5kW with the default pre 2000 figures.  And calculations from gas can be OK.  I read that they would be way out so I didn't do the calculations before my heat pump install.  But when the heat pump appeared to be oversized it was the only data I had at that time so I thought I would give it a go.  I didn't use the degree day method because I had a complete temperature record from inside and outside for every day.  Because I also had temperature records for all rooms I could be confident that the hall sensor was a good average of the whole house.  I plotted all the points and used a linear regression.  And also worked out the W per degree for the absolute worst gas usage day.  Scaling that to the inside/outside temperature difference at -3.2 gave me 5kW.  That's based on my boiler running at its specified efficiency of 65% - this was an assumption.  I should also add that I was not using gas for DHW at all.  The few datapoints I had for the heat pump were aligning with the gas and by mid winter it was clear that the same calculation for the heat pump was also 5kW.  Then I got a door blower test, it turns out my 1988 house is more air tight than a new build.  I used the measured ACH in heatpunk and the MCS spreadsheet models and both came out close to 5kW. 

@ashp-bobba Thank you for your reply, so does 'retro-fixes' mean fixing up other companies bad installs?

I am going to try to knock them down.  I've done some new break even calcs.  It would have been 6.5 years with the predicted SCOP, 8.7 with the poor SCOP and extra expenses I have incurred.  If I accept their offer it becomes 10.7 (assuming an improved SCOP), this is considerably longer than I had originally hoped. 

Oh, and do you know how much measured ACH or even ACH adjustments are used in the industry?  I get the impression they are not used much and some think that the default values are mandated.  It seems to be a huge blind spot.  Although one which Octopus, given their size and the number of issues they have had with oversized heat pumps, should have got to grips with by now.