Need Help Optimising My Rushed ECO4 Install: 12kW Bosch Heat Pump

Air Source Heat Pumps (ASHPs)

Last Post by Old_Scientist 3 weeks ago

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MickaMills

(@mickamills)

New Member Member

Joined: 3 weeks ago

Posts: 2

Topic starter 22/12/2025 4:39 pm

Hi, thought I would detail my ECO4 experience. I had a Heat pump installed back in April so this is my first winter, I have found several issues with the ECO4 install and would love any help getting the system to be the best it can.

The install was definitely rushed (1.5 days for a hybrid system), flow temp set at around 55 deg c, heating pump set at max speed, I have since set weather comp, and the pump much slower in auto setting making it much quieter running, water temp currently 36 deg at 10 deg c outside and house is 20.5 deg inside. The heat pump is a 12kw Bosch which I’d think is oversized and maybe short cycling, not sure what to do about that though as won’t be paying to swap it.

One other thing that concerns me is getting the system serviced as engineers seem few and far between where I live on the Llyn Peninsula North wales, I’d love to have the heat loss / radiators checked and the system serviced in the spring, any advice appreciated.

This topic was modified 3 weeks ago by Mars

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bontwoody

(@bontwoody)

Noble Member Contributor

Joined: 4 years ago

Posts: 969

22/12/2025 4:51 pm

Hi @mickamills . Welcome to the forum.

It sounds like you have made a good start on optimising you heat pump and yes it could well be oversized.

Do you have any previous energy usage figures you could use to compare. Also heat punk is quite easy to use as a heat loss guide.

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60

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Old_Scientist

(@old_scientist)

Prominent Member Member

Joined: 2 years ago

Posts: 321

24/12/2025 1:36 am

Welcome @mickamills

We too have an oversized 12kW Samsung heat pump installed on the ECO4 scheme. We cannot run continuously until outside temps fall to around 5C or below.

In milder weather (10-15C), we tend to run our heat pump more like a gas boiler, and find that turning it on for an hour or two as required is enough.

At temps of 5-10C, we turn off for 8-10 hours overnight which allows the heat pump to reheat the house during the day and allows for longer continuous running.

Once temps fall below 5C, we can run continuously, but we still tend to turn off overnight unless temps drop well below freezing.

We are pretty much able to run flow temps of 32-33C all year round, which is the lowest flow temperatures at which our radiators can emit the heat being produced (we may need to increase to 35C if temps fall below freezing, but we do not normally get below freezing daytime temps).

So overall having an oversized heat pump isn't the end of the world, and we still get excellent efficiency, primarily due to the low flow temps we are able to run at. Remember that you use relatively little energy in the spring and autumn, and most during the winter months when it is colder and your heat pump can operate continuously. An advantage is you may see less defrost cycles in very cold weather as your heat pump is not going to be working flat out tying to keep the house warm, but may only be ticking over at 50%

Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.

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