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What can I do to help the Mitsubishi Ecodan ASHP reach its service?

 
Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 3 months ago
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 Dockray
(@dockray)
Eminent Member Member
Joined: 3 years ago
Posts: 21
Topic starter 26/01/2026 1:39 pm   [#2781]

Hi

We have:

Mitsubishi Ecodan 8.5 ASHP

UFH throughout one storey building/ one zone - with 2 small radiators on a mezzanine

Installed 2022 (converted industrial building, very well insulated but not passive)

Weather compensation, 24/7

DHW  - on timer 2x a day

This system usually works a treat. LWT usually 29 at -2, keeps the house around 20-21 degrees. During the snow and ice during December/ New Year all was well.

But over the last few weeks the house has been getting colder and has been around 18.5-19 degrees. I’ve increased the LWT to 31 degrees and all the thermostats are set at 26 degrees to ensure the system can do its thing uninterrupted.

All the rooms, except the main room, are now reaching 21.5 but the main room is not getting above 19 degrees. Whilst this room is open plan and double height, this isn’t normal for it, its usually one of the warmer rooms. We’re due a service but they aren’t coming until March. There are also some new noises coming from the pipework, nothing major and not all the time. Before last years service we had an L9 error code.It was found we had a few micro leaks and the filter was quite clogged up. If this is still happening could this cause the current problem?

Our current flow rate is between 8 and 9. The pump speed is 4. I’ve checked the pressure gauges on the two UFH manifolds and the one that controls the main room is below 1 (approx 0.8) and the other one that controls the bedrooms/ bathrooms is at 1. At commissioning these were both at 2.

The flow meters for the main room are half the level they were when the photos were taken during commissioning, the others are lower but not considerably so.

The DHW has also been struggling to get to temperature. It's set to get to 48 degrees, morning and evening, and the timer is set to heat this within a 90 minute period, but at times it was only reaching high 30s/low 40s. Ive extended it it to 1hr 45mins, I’ve never had to do this before, but it is still sometimes struggling to reach it within the time. When necessary we’ve bumped the temperature up with the immersion heater. (We’ve also got a additional pump to get the water to the bathrooms, its a long thin building, and this is only on for 45mins in the morning and the same in the evening so we don’t waste the heat whilst it gets pumped around the building. Before minimising the time the pump was on for, the pump was reducing the water temperature, but it now has minimal effect).

Is there anything I can do myself to help it survive until the engineer comes in March? Ive checked the back of the ASHP to check there are no visible blockages and Ive been reading up on cleaning the filters, and i am willing to have a go at that but I don’t know how to top the system back up when i have emptied the filters, and i don’t know if that’s something I should be doing myself or whether I  should be leaving it to a professional. 

You can probably tell from my vague terminology I am well out of my depth but I”m willing to learn.

Thanks in readiness.



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4800
26/01/2026 2:02 pm  

Posted by: @dockray
↑

The flow meters for the main room are half the level they were when the photos were taken during commissioning, the others are lower but not considerably so.

I think that says that the filters are the first point of call

 

Posted by: @dockray
↑

I don’t know how to top the system back up when i have emptied the filters

It's the same procedure as with a boiler based system, if you know that.

 

Hopefully there are isolators near the filters so the amount you need to drain out is small.  

 


This post was modified 3 months 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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