Daikin 9kW to 8kW Swap Offer from Octopus

Matban · 2025-10-08T07:49:10Z

I had a Daikin 9kW installed in June 2024. I have been battling Octopus for it to be swapped for an 8kW since about October 2024. My primary issue with the 9kW has been noise. Secondary issues are overheating the house in moderate outside temperatures, low SCOP and the shockingly bad installation quality. I followed the typical 9kW owners path. Had it installed and right away noticed how noisy it was. It woke me up for the first overnight DHW Cycle and I wondered what on earth was happening. I soon re-programmed that for during the day and stopped it reheating DHW at all. I also noticed that despite the incredible racket it was constantly overshooting inside temperature. There was not a weather cure low enough. I installed an ESPAltherma and started monitoring it. Went on the open energy forum and facebook and found that there were other 9kW Daikin owners with the same issues. I had gas smart meter data and whole house temperature records from before the install so I calculated that the worst case gas boiler output extrapolated to -3.2 was 5kW. This seemed very low. I started plotting the heat pump output alongside the gas output on the same chart. The dots were aligning. Even though it was early days it looked like the heat pump heat output would also extrapolate out to 5kW. I presented this analysis to Octopus along with my prediction that the winter's SCOP would be 3 for CH at the end of October 2024 with my first request for a swap to an 8kW unit. This was declined. As the winter's data accumulated the heat output and SCOP were following the prediction. It was mind boggling that my actual heat loss could be 5kW and not the predicted 7.5kW. More research revealed that ACH might be the issue. I did a heat punk survey and googling to see what typical air exchanges might be for a 1988 house. This gave a good indication that ACH might be the issue. I commissioned a door blower test and it revealed that my house is actually very air tight. More so than most new builds. With the correct ACH figures, both heatpunk and MCS give around 5kW. All 4 methods gave pretty much the same value! And with default ACH my MCS and heatpunk surveys broadly agree with the Octopus figures. So all in all, even though I am not a qualified heat loss surveyor, I can state with a very high degree of confidence that my actual heat loss is 5kW at minus 3.2. This in my mind now all makes sense, the heat pump is a noisy model anyway, but it is made worse, has poor SCOP and is very hard to control properly because it is 78% oversized for the heat load. I've been feeding this information as it has built up to Octopus each time re-requesting the replacement but so far they have refused. The measures that have been taken include: Re-piping in the loft to stop resonation of the ceiling over a bedroom - moderate improvement but still noisy at 31l/m Removing the drip tray and building a soakaway 3 Daikin visits Many Octopus visits Repeated Survey - same result Further upsizing of radiators Latest outdoor unit firmware Pump speed set to 60% Issues not relating to the noise include 2 leaks during install - Resolved Clogged filter causing shut down twice - the system was not flushed - Resolved (through cleaning filter - not flushing) Radiators not balanced - Resolved by me Two burnt carpets - Resolved with £200 good will gesture Burnt Skirting - Not reported A section of lagging missing - twice, hidden inside the soffit so I didn't realise they hadn't fixed it the first time - Re-reported, fix being arranged Tap hammer, occurring after install, there was a PRV before the install with cold feeds balanced - Only just reported, not resolved Heating of volumiser during DHW. Resolved as part of the loft re-pipe External pipe lagging looked rough from day one but after a year has multiple gaps with the foam exposed, finishes short of the soffit board with a bit of silicone seemingly floating in the air. Recently reported - Offer to resolve One of the 28mm primaries is connected to the old 22mm boiler feed that loops out and back - Recently reported - offer to investigate Internal lagging gappy and loose in places - Offer to resolve Of course I would have expected some of the issues in the second list in such a big job. But given the overall catastrophic failure to install the correct sized heat pump and the sheer number of issues with the install I am including them in any complaints so that it is known just how bad the overall experience has been. When I was woken up on Sunday at 6am this week I had had enough. Over the next few days I started firing off emails to greg@octopus.energy notifying of external escalation and my handler, serving a formal rejection. I opened a section 75 claim with my credit card provider, also informing my handler. Also posted on the unofficial Octopus heatpump facebook where one of my posts was picked up by TJ who DM'd me. Yesterday I received a phone call followed up with the followi...

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Matban

(@matban)

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Joined: 3 days ago

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Topic starter 10/10/2025 7:03 pm

Posted by: @jamespa

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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.

Mine was £265. It would be cheaper for Octopus. They could train up their surveyors, it needs an accurate floor plan which they are capturing anyway. They probably need to just train up some of them and only do it on houses that are perhaps a bit bigger or of certain construction types. I bet they could get their software to work that out with AI. Then for those that didn't have a blower test, if it comes out over 7kW they could then do a blower test just to be sure. I guess they will stop installing Daikin's sooner or later, but people are still coming on the facebook groups saying a big Daikin has been specified. They also need to lobby for the regulations to be cleared up rather than hiding behind them. They are not fit for purpose if they are going to be used against customers like this.

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ASHP-BOBBA

(@ashp-bobba)

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10/10/2025 8:48 pm

@matban I would have to check the CIBSE guide as we have a software for this but its something like 3x for Kitchen and bathroom 2x for some other areas and 1.5 across the board in other areas but is subject to age of building and structure, as far as I am aware there is no adjustments we are allowed to make out of the recommended guide by CIBSE, we are kind of bending the MCS rules if we allow for less but in most cases where we have measured or have accurate measurement's they are nearly always much lower once a home owner has installed double glazing, installed a better letter box or changed the door to one without a letter box hole and have changed the doors to updated energy efficient doors, insulated walls, got rid of chimney balancing air bricks, sealed off the open fires and so on.

What we do is measure using air pressure loss equipment and get an accurate reading or base it on educated assessments knowing the results of many other installations or homes already tested. I think this is basically what the zero disrupt HG thing is doing, taking a very large pool of data and assessing the building being assessed against 30 others almost identical, this then makes a fast set of assumptions against proven data.

I still think every house should be pulse tested or air tested to be accurate and then add that air loos to the calculators and say add a spare 5% max for errors, this unfortunately costs around £300 per test and there is no appetite for customers to add more cost or companies to absorbe the additional costs.

AAC Group Ltd covering the Kent Area for design, supply and installation of ASHP systems, service and maintenance, diagnostics and repairs.
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