‘Heating Logic’ issues

[Gary C]

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.

[retsplines]

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

[nrb501]

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.

[CDubbs]

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+?

[albie999]

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

[CDubbs]

Thanks albie999

I’ll pass that onto my friend

[Gary C]

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!

[CDubbs]

Thanks for the update.

[Gary C]

UPDATE

I received this message, via the installers, from Fox late yesterday afternoon (23rd Jan)

"At present, we have prepared a special program to address this issue. We have completed the firmware upgrade on this unit and have enabled the battery heating function.

Based on the current situation, we recommend observing the system operation over the next few days to confirm the actual effectiveness of the program adjustment. In the meantime, we will continue to closely monitor this unit, and we will inform you should there be any new developments.

If you have any questions or notice any unusual behaviour during the observation period, please feel free to contact us at any time.

Thank you for your understanding and cooperation.”

I'm not sure exactly what the 'special program' entails, but looking at the firmware, the inverter Master is now 1.51, and the battery BMS is now 1.012.

I'm pleased to report that everything seems to be working perfectly at the moment. That said, the weather is mild at the moment, with nighttime temps of 8-9C on the south coast, so the real test will come during the next cold snap.

I shall continue to monitor it as Fox suggest, and post any further developments here.

In the meantime, kudos to Fox. It's taken almost two months and a lot of pushing, but when they get on something they seem to really go for it.

[Dave Foster]

I'm not sure exactly what the 'special program' entails, but looking at the firmware, the inverter Master is now 1.51, and the battery BMS is now 1.012.

In the meantime, kudos to Fox. It's taken almost two months and a lot of pushing, but when they get on something they seem to really go for it.

Latest BCU is showing as 1.011 so looks like you are seeing an early development release of 1.012 - fingers crossed

[albie999]

They patched mine with 0.013 ... Whatever that is when I had the battery heater problem

They said they will send to R&d so .. let's see

[Gary C]

I'm not sure exactly what the 'special program' entails, but looking at the firmware, the inverter Master is now 1.51, and the battery BMS is now 1.012.

In the meantime, kudos to Fox. It's taken almost two months and a lot of pushing, but when they get on something they seem to really go for it.

Latest BCU is showing as 1.011 so looks like you are seeing an early development release of 1.012 - fingers crossed

Thanks Dave. Fingers are indeed very firmly crossed!

[maccoylton]

I have this issue also, but am getting no comms from Fox, last emailed them on 14th Jan. Looking at my data, it my case it appears to happen when in self use mode, the battery requires heat, the battery state of charge is at or below 40% and there is a little but not a lot of solar. So it appears to be when switching power source from battery to another source. If there is a lot of solar it seems to heat ok, if there no solar it appears to heat ok. When it happens if I isolated the PV, the heater kicks in and then I can switch my PV back on.

[Gary C]

I have this issue also, but am getting no comms from Fox, last emailed them on 14th Jan. Looking at my data, it my case it appears to happen when in self use mode, the battery requires heat, the battery state of charge is at or below 40% and there is a little but not a lot of solar. So it appears to be when switching power source from battery to another source. If there is a lot of solar it seems to heat ok, if there no solar it appears to heat ok. When it happens if I isolated the PV, the heater kicks in and then I can switch my PV back on.

Sorry to hear that you're having these problems and getting no response from Fox. Although your issues sound different to mine, which could happen at any time of day or night, regardless of PV or SoC, I too suffered the same lack of response.

It's incredibly frustrating, but persistence does pay off, and I found that when they eventually did respond, they got on the case and, after trying a few different things, came up with what I hope is a fix. (It's early days yet, but I've had no problems since last Friday.)

I don't know what inverter or battery you have, but my fix involved updating the inverter firmware to the latest versions, and updating my EP battery's firmware to version 1.012, which appears to be a brand new, as yet unreleased version.

It may be that this will be the solution for you. But first, you've got to get Fox to respond, so keep at them!

Good luck - and keep us updated.

[albie999]

It may be that this will be the solution for you. But first, you've got to get Fox to respond, so keep at them!

Good luck - and keep us updated.

Hey Gary, you say they have "fixed" your problem .. but have you (with the slightly warmer temperatures), been able to see if the battery heater is now working. I am also on v1.012 ... but the one day (since I had that firmware), where the temps dropped below the warm up settings .. I did not get the "reboot" problems .. but I also did not get battery warm up from the battery charge "unless" I switched on the "heat from grid"

[Gary C]

It may be that this will be the solution for you. But first, you've got to get Fox to respond, so keep at them!

Good luck - and keep us updated.

Hey Gary, you say they have "fixed" your problem .. but have you (with the slightly warmer temperatures), been able to see if the battery heater is now working. I am also on v1.012 ... but the one day (since I had that firmware), where the temps dropped below the warm up settings .. I did not get the "reboot" problems .. but I also did not get battery warm up from the battery charge "unless" I switched on the "heat from grid"

I have indeed. I have Battery Warmup in the app set to kick in as soon as the battery drops below 9C at anytime between 00.00 and 23.59 (heat from grid), which it has been doing without any problems since last Friday (though it's not been really cold, night temps have been below 9C on a few occasions).

It's still in the monitoring stage (Fox say they're 'keeping an eye on it'), and I've been asked to report back if there are any issues, but so far, so good.

[albie999]

Interesting that you say you have the "heat from grid"function switched on 24hrs, as when I have that on ... Mine also works

However, the function on the battery is supposed to be able to heat itself when the battery is above 40% charged without needing heat from grid enabled, it is that functionality that does not seem to be working at the moment, therefore you potentially have to spend money to heat from grid rather than from the batteries own reserve

[Gary C]

Interesting that you say you have the "heat from grid"function switched on 24hrs, as when I have that on ... Mine also works

However, the function on the battery is supposed to be able to heat itself when the battery is above 40% charged without needing heat from grid enabled, it is that functionality that does not seem to be working at the moment, therefore you potentially have to spend money to heat from grid rather than from the batteries own reserve

That function has never worked on mine to my knowledge, but not much else did, either, so I never got the chance to check it out properly.

I've only had a fully functioning system for four days now, and for now I'm happy to heat the battery from the grid, as in these grey days the times I need it to be warm are always when it's below 40%. I'd much rather spend a little bit extra rather than wake up in the morning to find out the battery hasn't charged overnight because it was too cold. That happened far too many times with my unheated EP5, hence the upgrade to the EP12+.

In retrospect, if I'd known it would result in two months of grief I'd have stayed with an unheated model and built an insulated enclosure, or something.

[CDubbs]

Just to add, having an heated EP11 outside, once I built a 50mm insulated box around it, the lowest cell temp has never dropped below 10C, and the heater has not had to kick in.
My friend with the same battery but having the heater issues, where its stops working when the heater tries to kick in, got me to help him build a 50mm box 2 weeks ago, and for the first time this winter has a working battery 24/7 and that’s with battery heating disabled until Fox roll out a fix fully.
So conclusion is, insulated box is all you need, even outside.

[Gary C]

Just to add, having an heated EP11 outside, once I built a 50mm insulated box around it, the lowest cell temp has never dropped below 10C, and the heater has not had to kick in.
My friend with the same battery but having the heater issues, where its stops working when the heater tries to kick in, got me to help him build a 50mm box 2 weeks ago, and for the first time this winter has a working battery 24/7 and that’s with battery heating disabled until Fox roll out a fix fully.
So conclusion is, insulated box is all you need, even outside.

Thanks for that. It's reassuring to know.

Is there any chance that you could post a picture of your insulated box? It's something that I may just do anyway - especially if there are any more shenanigans!

[CDubbs]

This cover is over a metal cover I had made for the battery, so it’s bigger than the one I made for my friend, that one went straight over the battery.
Picture before and after waterproof membrane attached.

[MaterialBarracuda48]

This cover is over a metal cover I had made for the battery, so it’s bigger than the one I made for my friend, that one went straight over the battery.

Thanks for the helpful post.

To help others that might be looking to do the same as you/similar, what sort of temperatures was you seeing in the past compared to now? As you may know, mine is inside the garage with a blanket over it, and has not done a single heating cycle for around 3 weeks, and after last night it is at 12.5°C.

[Gary C]

This cover is over a metal cover I had made for the battery, so it’s bigger than the one I made for my friend, that one went straight over the battery.
Picture before and after waterproof membrane attached.

IMG_2335.jpegDFD81300-9C61-459A-9615-B67A8A8CDE26.jpeg

Many thanks for posting the pics. That's a big help.

[CDubbs]

I was dipping into the single digits
So battery heater was kicking in at 9 and going 15
Now never gets that low, so heater not kicking in
Currently outside temp 2C lowest cell is 17
Pic of current overnight temps from midnight and current max/min cell temps
On warmer nights recently have seen max cell temp at 25 in the morning 6 hours after grid charge has stopped

[MaterialBarracuda48]

I was dipping into the single digits
So battery heater was kicking in at 9 and going 15
Now never gets that low, so heater not kicking in
Currently outside temp 2C lowest cell is 17
Pic of current overnight temps from midnight and current max/min cell temps
On warmer nights recently have seen max cell temp at 25 in the morning 6 hours after grid charge has stopped

Perfect!

That will be really helpful for those needing to know if it is worth doing.
Also, being above 20°C, the charge and discharge rates are 100% max, handy if you did need a full draw on your system.