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My NIBE ASHP Nightmare: No Commissioning, High Bills and a Hostile Installer

Mike @ Camelot · 2026-01-22T09:26:49Z

Hello Forum. Background. I am building a 150sqm bungalow using Passive House as a guide in Devon. Excellent thermal insulation. 0.9 ACH. Zender MVHR. NIBE F2040-12, SMO 20, Megacoil 300L. UFH from Wunda, Rapid Response (about 800 metres in 13 loops) The system (ASHP)was installed in September 2025 by a NIBE accredited installer. I never received any commissioning paperwork or handover instructions. The installer is very difficult to deal with. I have been asking if the BUS Grant has been submitted, and for some adjustments to be made to my system. In a one sided phone call last week he launched into a vitriolic tirade that accused me (amongst other things) of being a trouble maker. I still have no paperwork. When I ordered the system, his website stated he was MCS accredited. He has since allowed this to lapse and is using an umbrella company. He refused to say whether the BUS Grant application has been submitted, and would not tell me the name of the umbrella company. The installer did not complete any heat loss/heat load calculations, and as a result I now believe that at 12Kw the ASHP is oversized. At the time I was completely ignorant of the steps that should be taken prior to starting an installation. Judging by the number of comments on the forum this seems to be a common mistake. My first utility bill showed a usage of approximately 600kwh. I asked my installer why it was so high. He felt that was ok for an “electric” house. Since I was unable persuade the installer to look at my system I decided I would have to learn how to adjust it myself. With the help of the Open Energy Monitor Forum, John Cantor’s book, the Ultimate Guide book, and many hours on YouTube I have a better understanding of how ASHP work and how they should integrate with UFH. Changing my system settings by small increments at a time I have been ablet to reduce my power usage by approximately 50%. However, I believe that further savings are possible. A volumizer has been included in my system, but it doesn’t seem to have been installed as shown in the Installation Manual. Also, it is not in line with the information on this Forum. I would greatly appreciate it if members could look at the attached photograph, and schematic and post their conclusions.

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Air Source Heat Pumps (ASHPs)

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 4840

11/05/2026 8:18 pm

Posted by: @mike-camelot

↑

don't have a room (central) thermostat. That was actually my question. My system has been working quite well while the OAT has been cool. Now we are seeing higher temperatures I was considering fitting a central thermostat (NIBE BT 50) so that I could set it to a temperature that would more efficiently reflect the demands of the house. I was asking for feedback from anyone who may have this unit fitted

It may be a bit house dependent. In my first year I used pure weather compensation without any room influence for almost all of the season, except at the end where I used the sensor in the heat pumps own controller as a temperature limiter to deal with excess solar gain in March/April. This year I haven't done that, its just on pure WC even now (I switched it back on today). In between last year and this I tweaked the high oat end of the WC curve so the min permissible ft is a few degrees lower.

I did, very early on, try using the temperature sensor as a controller layered on top of reasonably well adjusted wc, but it was a very poor way to control, resulting in much greater temperature swings and far inferior comfort than pure WC, nearly as bad as when I was running a boiler at the high flow temperature so favoured by plumbers!

Hope that helps

This post was modified 36 minutes ago by JamesPa

This post was modified 35 minutes ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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