FoxESS Community - Owners & Installers Forum

Long story short(ish), last November (2025) I upgraded my unheated EP5 battery with a new heated EP12+.

All seemed well for a few days. Then the (brand new) inverter started going down and into a ‘loop of death’ for long periods (sometimes 12 hours or more). [See video in link below]

https://drive.google.com/file/d/1S5RXo- ... sp=sharing

As you’ll see, the display reads “Waiting…” for 30 seconds or so, then it goes blank, then it reads “Starting…”, and then the cycle repeats endlessly for hours on end. This is accompanied by a sort of ‘knocking’ noise, which you can just about make out on the video. Because the inverter is mounted on my bedroom wall, this makes sleeping difficult.

After six weeks, during which Fox tried mixing and matching various vintages of firmware versions, they eventually came back, via the installers, with this response:

“We have confirmed that this issue is related to the battery warm-up function and are currently investigating the root cause.
To mitigate the issue for now, we will suggest to disable the warm-up function on the user's side. We acknowledge this is only an interim measure and are actively working on a permanent solution.”

Then, after more pushing from the installers, who have been brilliant, yesterday they came back with this:

“Confirmation of the Issue
We have received a limited number of reports regarding similar behaviour with the EP12+ (with heating function) under certain conditions. However, this does not appear to be a widespread compatibility issue between the EP12+ and existing inverters at this stage.
Root Cause & Solution Timeline - Current Progress: Our technical team is actively investigating the root cause. Based on preliminary analysis, the issue is likely related to the heating logic of the battery under low-temperature conditions, which may be resolved through software optimization.
Solution Path: We aim to finalize the root cause by the end of this week (by 23rd Jan.). If confirmed as a software-related issue, we plan to provide a fix via remote firmware update (OTA), with a target to release the update by the end of this month.”

So, although it’s taken far too long to get to this stage, at least Fox has acknowledged that there is an issue, and is working to fix it.

I’ll post an update as soon as I hear more, but in the meantime it would be interesting to hear if anyone else has experienced similar issues.

I also experienced this on my KH7 + EP11.

Disabling the timed "Warmup Slot in low price" function (the time schedule where grid power is permitted to heat the battery) "solved" it for me. I still have warming turned on but only allowed to use PV (or battery energy when >40% SoC).

Hopefully there's a fix soon!

- Ret

Good to see this issue is acknowledged and a solution is hopefully in the pipeline, I think it may affect all the heated EP series as I've seen (and reported) this on my home system as well.
Unfortunately we then need another period of very cold weather to see if they have actually fixed this.

My friend has a heated EP11 and 3.7 H1 G2 inverter fitted new in October.
The heated function has never worked, when it does try to kick in, all power is drawn from the grid and the battery goes offline, and although the app icon showing the heating function working, it does not heat the battery, in fact the cells just get colder.
The only way to get load supplied from the battery is to turn off the heating function in this scenario.
So the battery works and charges ok until the heating function kicks in.
Fox and the installer have been fairly clueless as to what to do.

Is the this the same issue you e seen on the EP12+?

I have had all the same issues, which is on a very long thread in the forum now (viewtopic.php?t=1603) ... and Fox have been trying various firmware updates to my system, including the latest 0.013 (apparantely the naming convention is right .. someone must have had a typo) .. however, even with this version .. I still suffer from the issue that .. if I do not have "warm from the grid" selected, even if there is excess PV .. it still will not warm the battery

Fox have told me (on Monday) that they have sent this to the R&D team .... so I will give it a week .. then chase them up

Thanks albie999

I’ll pass that onto my friend

CDubbs wrote: ↑Thu Jan 22, 2026 3:18 pm My friend has a heated EP11 and 3.7 H1 G2 inverter fitted new in October.
The heated function has never worked, when it does try to kick in, all power is drawn from the grid and the battery goes offline, and although the app icon showing the heating function working, it does not heat the battery, in fact the cells just get colder.
The only way to get load supplied from the battery is to turn off the heating function in this scenario.
So the battery works and charges ok until the heating function kicks in.
Fox and the installer have been fairly clueless as to what to do.

Is the this the same issue you e seen on the EP12+?

Yes, I've had this - and many other issues, including BMS alarm codes, and more, but the main one is as described above, where the inverter goes into the “Waiting… Starting… “Waiting… Starting… …” loop for lengthy periods, accompanied by a knocking sound, during which the battery and inverter are both down, the battery fails to charge, and the SoC drops down to 7 or 8%.

From what others have said, it appears that this could be a problem affecting not just the EP12, but all heated models in the EP range.

The current situation with my EP12 is that, since Fox disabled the heating function earlier this week, the battery has been charging and discharging okay, but is obviously compromised by the cold and not doing so to its full capacity.

Now Fox has acknowledged the issue, and says it's working on a solution, I guess all that any of us with these problems can do is wait.

They've told me that they aim to have it resolved by the end of January, and I do hope so, as one of the main reasons I bought this battery was because of its heating function, and if it turns out that this doesn't work, then for me, the product is not fit for purpose.

Fingers crossed!

Thanks for the update.