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New Build ASHP Defects - Looking for Advice, Support & Shared Experiences

 
Air Source Heat Pumps (ASHPs)
Last Post by Newby 2 hours ago
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 Newby
(@newby)
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Topic starter 07/03/2026 4:08 pm  

Hi everyone,

I’m hoping to get some advice from people who’ve been through similar problems with new‑build ASHP systems. I’ve recently moved into a 2025 new‑build with a Daikin heat pump, UFH downstairs and radiators upstairs, and the system just isn’t performing anywhere near what it should.

Rooms are sitting at 14–16°C in winter, bathrooms and the utility are even colder, and the UFH floor only ever feels lukewarm. After months of going back and forth with the developer, it’s becoming clear that the issues aren’t “settings” or “user error” — they’re design and commissioning problems.

The more I’ve learned, the more I realise how much was never done properly. Heat loss and radiator sizing are only the starting point. A proper heat pump design should also include things like:

  • Hydraulic design (flow rate at design conditions, delta‑T, pipe sizing, velocity, pressure loss)

  • Pump capability (can the internal pump actually deliver the required flow at the system head?)

  • Domestic hot water design (coil sizing, recovery time, realistic flow temps)

  • Controls strategy (weather compensation curve, zoning, room influence)

  • System volume (minimum water content to avoid short cycling)

  • Defrost and bypass strategy (how flow is maintained during defrost)

  • Part‑load behaviour (how the system modulates most of the year)

None of this was done on my install. The developer used boiler‑era assumptions, applied a 0.33 “correction factor” to the radiator sizing, and never checked whether the pipework or pump could actually deliver the required flow. Upstairs radiators are single‑panel, bathrooms have towel warmers instead of emitters, and the UFH loops were never balanced.

To make things worse, thermal imaging has shown missing insulation, cold bridging and wind‑driven heat loss — so the actual heat loss is higher than the SAP design assumed.

I’m now dealing with NHBC and looking at getting an independent M&E engineer involved, but before I go further I wanted to ask:

  • Has anyone else had similar issues with new‑build ASHP systems?

  • Did you manage to get a proper redesign or remediation?

  • Any recommendations for independent heat‑pump engineers or M&E consultants (North West)?

  • Anything you wish you’d known earlier in the process?

I’m not looking to over‑engineer anything — I just want a system that’s designed properly and actually works in winter. Any advice or shared experiences would be really appreciated.

Thanks in advance.



   
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