Advice for a novice on Mitsubishi Ecodan 6kW

Green_Fox · 2026-01-05T14:03:44Z

Hello all, I am very much hoping to draw on the expertise and good will of the RHH community as my partner and I seek to understand our Ecodan setup. I am a complete novice and am trying to act like a sponge and soak up as much advice and support as possible in the hope that I can pay that back in due course. *** Bottom line upfront: we’ve just moved into a new build 4 bed semi in rural Fife. It’s an EPC A (98) with UFH, 12 solar panels & Fox ESS battery, and Ecodan ASHP. Sounds like a green energy dream, right? I wish…! A big part of the problem is that we moved into the property in December when everyone was knocking off for Christmas. As a result, no one has walked us through the Ecodan controls. The solar and battery are a mystery to us as, again, the installer hasn’t yet walked us through anything. I don’t even know if or what they’re connected to, although the Fox ESS display is on. We’re in the middle of a cold snap here and, having come from a gas boiler property ‘down south’, we’re having to get to grips with the system quickly and clearly very inexpertly. Immediate problems Lukewarm radiators upstairs: details on property and setup provided below, but temperature upstairs is set to 22c in day time with set back to 19c overnight (programmed via FTC7 and on a weather compensation curve). The upstairs struggles to get anywhere near 19c in the day time. Sky high consumption and delivery: In Jan 2026, 170 kWh consumption (16 DHW / 153 Heating) and 455 kWh delivered (37 DHW / 418) so far. This seems absolutely eye watering for five days use, particularly as there’s only two of us in the property with relatively modest temperature requirements. In December, the KwH delivered was around 2500! As you can imagine, we are petrified of the incoming bills. Auto Adapt error: when I try and switch the control function from compensation curve to AA, the FTC generates a P1 code after 2-3 mins. Property details 4 Bedroom semi-detached. Around 180 sqm. Downstairs: fairly open plan, but with separate utility room, hallway area, and downstairs shower room. UFH downstairs with Heatmiser thermostats in each room plus wood burner in living room. Upstairs: four bedrooms (including a north-facing gable end), one main bathroom, two en-suites. Rads upstairs (with a Mitsubishi RC wireless). I think all rads are TRV. UFH in bathrooms and heated towel rails. Fenix thermostats for the three upstairs bathrooms. To my eye, there is a lot of thirty party kit here. I’ve de-programmed the Heatmisers so they’re effectively ‘dumb’. I manually set the temperature to 22c in day and then set back to 19c overnight and leave them alone aside from that. I haven't done much with the bathrooms thermostats aside from setting them to 19c and leaving them. Hardware Ecodan 6kW PUZ-WM60VAA with FTC7 controller & 300l water tank Mitsubishi wireless RC UFH (may need some guidance on how to provide details on this, i.e. manifold, valves etc) Solar + Fox ESS battery (not setup yet, so not benefitting from the meagre solar we’ve had the last wee while) Current setup DHW set to ‘eco’ tank temperature is set to 48c with max temp drop of 10c Scheduled to heat up for three blocks: 5-6am; 12-1pm; 5-6.30pm. I appreciate this is probably very inefficient and egregious. While not very ‘green’, we both have a bath every other day and we’re struggling to ensure enough hot water even with a 300l tank. Heating Downstairs: manually set the Heatmisers to 22c in day time with a manual set back to 19c overnight (from 2200-0700). I know they shouldn’t be treated like normal thermostats, so I’ve tried to keep it as low, slow, and simple as possible. If forum colleagues can think of another way of managing this in the short term then I’m all ears! Upstairs: schedule is 0000-0600 @ 19c; 0600-2200 @ 22c; 2200-2400 @ 19c. I’m using the WC curve control for this. The curve is 48c / -3c and 31c / 13c. As mentioned above, I’m struggling to get the upstairs above 19c. It’s usually hovering around 18.5c. I think part of the reason for this is the large master bedroom, which is a north facing gable end. It’s got a large rad, but seems very hard to keep warm. Some indicative data No idea if any of the below is useful, but some stats below: Pump setting: 5 for DHW / 5 for Heating (I haven’t messed with these since the system was installed) Current flow rate at 1100hrs on 5/1/2026: 28 Thermistor Readings on 5/1/2026 @ 1103hrs TH1A 18c THW1 29c THW2 28c THW5a 43c THW5b 43c TH7 1c *** I welcome any advice that forum colleagues might have. I’ve got the MEL app downloaded so if you need me to provide any screenshots then let me know. Similarly, happy to take photos of the inside and outside units if that would be useful. As I say, very very new to this, so treat me like a primary school kid! GF

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Majordennisbloodnok

(@majordennisbloodnok)

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09/01/2026 9:08 pm

Whilst I agree with @sheriff-fatman’s point, I checked my Ecodan and found on 6th it was indeed defrosting about once an hour from late morning. Although it had been pretty cold the night before, the defrost cycling was whilst the temperature was hovering around one degree.

We all know the real enemy of heat pump performance isn’t the cold as much as the damp, so my guess for the hourly cycling of mine was damp air oscillating around the threshold between ice and vapour.

Could it be similar for your heat pump, @green_fox?

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solum profundum variat"

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Sheriff Fatman

(@sheriff-fatman)

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Joined: 9 months ago

Posts: 169

09/01/2026 10:02 pm

Posted by: @majordennisbloodnok

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Whilst I agree with @sheriff-fatman’s point, I checked my Ecodan and found on 6th it was indeed defrosting about once an hour from late morning. Although it had been pretty cold the night before, the defrost cycling was whilst the temperature was hovering around one degree.

We all know the real enemy of heat pump performance isn’t the cold as much as the damp, so my guess for the hourly cycling of mine was damp air oscillating around the threshold between ice and vapour.

Could it be similar for your heat pump, @green_fox?

Fair point. The highest frequency of defrosts I'd seen so far had been 6 within a 24 hour period, but my sample size of relevant data is very small.

130m2 4 bed detached house in West Yorkshire
10kW Mitsubishi Ecodan R290 Heat Pump - Installed June 2025
6.3kWp PV, 5kW Sunsynk Inverter, 3 x 5.3kWh Sunsynk Batteries
MyEnergi Zappi Charger for 1 EV (Ioniq5) and 1 PHEV (Outlander)
User of Havenwise (Full control Jun-Dec 2025, DHW only from early Dec)
Subscriber to MelPump App data via CN105 Dongle Kit

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