John,
I am just here to tell people how I flagged my issue and the proof I provided up front.
I have worked for 15 years in customers facing software/ IT support and a year in an R&D role.
If you go to a company and say ‘i think it’s broke’ they may investigate but may also say ‘you don’t know about this we are the experts, it’s all ok’.
If you go to a company with two heat loss survey’s (or even just heatpunk calculations), evidence of your actual heating usage (over a long extended cooler period) and system data, then provide a solution showing exactly what needs to be changed they are a lot more likely to listen to you and hear you out (trust me this works in most industries).
I not only specified the heat pump change but due to the specific circumstances I also specified 5 radiator changes including a new K3 500 *2400.
Not only was I listened to but as I had done all the background work it was easy to get both the senior engineer and one of the directors on board and get the system designed to work as I wanted (40°c flow rate made possible by the smaller pump and radiator changes).
I am glad you have identified this issue and I really want anyone with one of these beasts to be able to get it swapped and have a SCOP in the high 4’s too but as Matt has said, it is Octopus you need to convince and while a one off calc works for me it may take a bit more proving to get the right people in after sales to budge.
If you don’t want to do the above you can try and call up and tell them it is running inefficiency and you believe the heat loss is wrong and ask them to check it, however unless you know what sizes the windows and doors were listed at and how much loft insulation the original surveyor specified you may not get too far.
The other point to be aware of is that octopus usually only specify a cop of 3.6 for the big unit and if you are getting this (even if it is not optiomal) they can say it is as designed.
If you then want to argue it is not operating efficiently as it should be due to being oversized contrary to part L of the building regulations (part L volume 1 section 5.8(b) " b. A sizing methodology that takes account of the properties of the dwelling, such as the
Chartered Institute of Plumbing and Heating Engineering’s Plumbing Engineering Services
Design Guide.
Systems should not be significantly oversized.") you would need to show that it is in fact significantly oversized.
Sorry if the above is a bit long and dull in places and I am not here to bash anyone, just want to see a few more people climbing up the SCOPs and start showing everyone these things can actually work if you size end install correctly.