Fox ESS Error Code-1 No Utility, Error Code-26 Grid Voltage Fault, Error Code-27 Grid Frequency

[Wolfenden12]

So I wasn’t looking in the right place! The breaker had tripped so I reset it and all was fine for 2 days, happened again yesterday and today. I’ll call installer tomorrow but what could it be? Seems to start when I force charge battery overnight? I also have an ashp that has been running more as it’s so cold, shall I just leave the breaker off and should I be worried?

[Dave Foster]

So I wasn’t looking in the right place! The breaker had tripped so I reset it and all was fine for 2 days, happened again yesterday and today. I’ll call installer tomorrow but what could it be? Seems to start when I force charge battery overnight? I also have an ashp that has been running more as it’s so cold, shall I just leave the breaker off and should I be worried?

If it is happening when charging it is very likely the breaker is not rated correctly or is faulty - what inverter size do you have, and can you have a look at the breaker and see what it’s rating is (B16, B20 etc.. or post a picture of the breaker)

For now leave the breaker on, once I know the rating if you have access to the inverter panel and don’t mind going into settings we can change the max battery charge current which should stop it from popping until the installer comes out.

[RobSweeney]

Hi

This error has occurred on my system which I have reported to provider. I've looked at Solar and main breaker, nothing was tripped, but switched the solar trips off and on. Still getting the error message. What steps should I take next?

Thanks

[Dave Foster]

Hi

This error has occurred on my system which I have reported to provider. I've looked at Solar and main breaker, nothing was tripped, but switched the solar trips off and on. Still getting the error message. What steps should I take next?

Thanks

The error means there is no mains voltage being recorded by the inverter, so possible a faulty MCB or RCD feeding it (try switching them off then back on again) - if that still fails to register it could be a wiring fault / loose wire in the AC connector and that is best left for an electrician to investigate.

[if42]

Hi
Newly installed KH10.5

I tried a force charge (which I am not entirely sure what this does other than charge from the grid?)

This seems to have started and then stopped, and the fault codes 1, 26, 27 are now set.

I see in the pinned / top post here that the MCB sizing may be wrong for my inverter, see attached screenshot - I think that's the MCB?!?

I tried restarting the inverters, DC off, AC off, Battery off, wait for inverter to power down, and then all back on - but it did not solve the fault states - I did not as yet flip the PV MC as shown.

Any tips welcome!

Thanks!

[Dave Foster]

Yes that is underrated, it should be at least a 50A breaker - you’ll need your installer back to fix that.

Disable any force charge you have set and then turn the breaker back on again.

You can do a temporary fix to throttle max power the batteries are charged at, you’ll need to know your battery voltage which you can find at the inverter panel in System, Battery - then once you have it you can go into the inverter settings, battery, max chg current.

The charge current is the DC amps not AC amps that’s why you need to know the battery voltage - you want to reduce the charge current to (say) 4000 watts so you divide 4000/battery volts and that will tell you what to set the max chg current to (the default is 50)

4000 watts will be approx 17A (AC) which is well within the 32A breakers limits

[Will]

in the meantime while you're waiting for your mcb to be upgraded to a larger one you can set the inverter limit to 70% so it's stays within the 32amp limit.

[reef]

I suspect this undersizing is rather common unfortunately. My installer only installed a 20A breaker on my H1-5.0-E.

It hasn't tripped in 2½ years but isn't ideal.

[if42]

Thanks very much!

I contacted the installer and they have come and changed the MCB and also the cable between the inverter and the consumer unit, which they said was also under rated.

Regarding force charging, are there "good" current rates to set or should I leave the defaults and lets the BMS handle it?

[pm]

We've had this trip three or four times in the last few months
Inverter is inverter H1-6.0-E and the Trip is 32A

When reset, the system works normally again.

In at least two of these cases, the first error seems to have been logged at around 01:00. We don't charge the battery from the grid.
Any thoughts?

[Dave Foster]

We've had this trip three or four times in the last few months
Inverter is inverter H1-6.0-E and the Trip is 32A

When reset, the system works normally again.

In at least two of these cases, the first error seems to have been logged at around 01:00. We don't charge the battery from the grid.
Any thoughts?

Is it a 32A MCB or RCBO one is simply a circuit breaker (and unlikely to trip unless faulty), the other will trip if it detects too high a leakage current.

If it is an RCBO it will likely be rated a 32A and RCD at 30ma - this can cause trouble, the reasons are complex but humidity is a part of it and that would be high at 1am - Fox recommend that and RCD (RCBO) should be rated at 100mA.

[pm]

We've had this trip three or four times in the last few months
Inverter is inverter H1-6.0-E and the Trip is 32A

When reset, the system works normally again.

In at least two of these cases, the first error seems to have been logged at around 01:00. We don't charge the battery from the grid.
Any thoughts?

Is it a 32A MCB or RCBO one is simply a circuit breaker (and unlikely to trip unless faulty), the other will trip if it detects too high a leakage current.

If it is an RCBO it will likely be rated a 32A and RCD at 30ma - this can cause trouble, the reasons are complex but humidity is a part of it and that would be high at 1am - Fox recommend that and RCD (RCBO) should be rated at 100mA.

Here is the box (sorry, not an expert at all)

[pierpand]

Thanks Will for this very timely post

I experienced this on Sunday in pouring rain during storm Bert The breaker tripped and I reset, but it tripped again a few minutes later. After retetting for the second time (after the force charge session) it has been been fine ever since. I initially thought it may have been caused by a surge related to the storm but aftyer reading your post I remember that at the time I was force charging (programmed to take advantage of a free power session from Octopus) so possibly this was the trigger?

I have a recently installed 3.6k FoxH1 inverter, 11 440w CS panels and a Fox ESS 5kw battery with a B20 breaker.

This has happened once before, not during a charge event

Any thoughts?

Anthony

Ciao il mio Invert mi da lo stesso errore,ma interuttori sono tutti alzati

[pierpand]

Thanks Will for this very timely post

I experienced this on Sunday in pouring rain during storm Bert The breaker tripped and I reset, but it tripped again a few minutes later. After retetting for the second time (after the force charge session) it has been been fine ever since. I initially thought it may have been caused by a surge related to the storm but aftyer reading your post I remember that at the time I was force charging (programmed to take advantage of a free power session from Octopus) so possibly this was the trigger?

I have a recently installed 3.6k FoxH1 inverter, 11 440w CS panels and a Fox ESS 5kw battery with a B20 breaker.

This has happened once before, not during a charge event

Any thoughts?

Anthony

Ciao il mio Invert mi da lo stesso errore,ma interruttori sono tutti alzati

[MagicDude4Eva]

That the cause is your circuit breaker is not necessarily the only reason. I had the following faults and asked support for an explanation:

Code: Select all

INVERTER	--	Grid Frequency Fault	Inverter	2025-07-15 07:54:42 CEST	2025-07-15 13:46:39 CEST
INVERTER	--	Grid Frequency Fault	Inverter	2025-07-14 10:22:06 CEST	2025-07-14 14:48:58 CEST
INVERTER	--	No Utility	Inverter	2025-07-07 05:12:06 CEST	2025-07-07 05:34:39 CEST
INVERTER	--	Grid Voltage Fault	Inverter	2025-07-07 05:12:06 CEST	2025-07-07 05:34:39 CEST
INVERTER	--	Grid Frequency Fault	Inverter	2025-07-07 05:12:06 CEST	2025-07-07 05:34:39 CEST
INVERTER	--	DC Bus volt is high	Inverter	2025-07-07 05:06:08 CEST	2025-07-07 05:12:06 CEST
INVERTER	--	No Utility	Inverter	2025-07-07 04:04:34 CEST	2025-07-07 05:06:08 CEST
INVERTER	--	Grid Voltage Fault	Inverter	2025-07-07 03:57:40 CEST	2025-07-07 05:06:08 CEST
INVERTER	--	Grid Frequency Fault	Inverter	2025-07-07 03:57:40 CEST	2025-07-07 05:06:08 CEST

There analysis provided that on the AC-side of the inverter there was an issue with the grid-provider. It is noteworthy to say that during that the (such as "No Utility") we recorded no supply interruption or breaker tripping. The support explanation was that the inverter into "safety mode" goes and restores once the frequency normalised via the grid-provider.

[AntonioVentrice]

Esiste un manuale con tutti i codici di errore?

[Mtsuleman]

I had this happen to me do the first time a few weeks ago when the weather was bad. So started to look into this and noted that my installation has a 32A type B breaker.
I also noted that when the breaker went, the house lights etc were fine which leads me to think that the MCB may have been the culprit. So looking into it further I have read that a Type C breaker should have been installed as it has slightly looser tolerances but still within Fox recommendations.

Does any body else have any steer on this? Is replacing with a type C breaker likely to work?

[StevePre]

Hi All,

I am suffering from the same three fault codes. The mains breaker had tripped. I reset that and rebooted the inverter as per the instructions (twice).

The breaker remains made (ie it hasn't tripped again) but I'm still getting the error messages and there's no sign that the inverter can detect mains supply or the house load.

The battery is fully charged but the inverter isn't using it to service the house load.

When the sun is shining the solar panels are still supplying the house and returning electricity to the grid where PV production exceeds the house load (I can see this on my smart meter).

I have raised a ticket with Fox, but an ideas in the meantime would be very welcome.

Thanks in advance

Steve

[Dave Foster]

There's definitely something wrong with the grid side of the inverter, those 3 errors come together when the grid connection is missing.

It's possible you have a wiring fault or a bad breaker (try opening and closing it again), sometimes there is an AC rotarty isolator switch fitted between the breaker and the inverter - check that as well.

If you cannot find an obvious fault, you need to contact your installer or an electrician as it is likely the breaker is faulty or there is a wiring fault between there and the inverters AC connector on the lower far right hand side of the inverter.

[StevePre]

Thanks Dave, that makes sense. Thank you for taking the time to reply.

How frustrating though!

[StevePre]

The weird thing is though - when I first tried to reset the inverter, it wouldn't start up again until I found the tripped breaker and remade it. Once I had done this it flashed back up and indicated normal function, but wasn't detecting the mains supply or domestic load.

So, there is obviously some connection to the mains supply through the breaker. Nonetheless, I have reset the breakers again.

There also seems to be a signal line that goes up with the power cables connected to this toroidal ring sensor (see picture) I gave the little connector block a wiggle to see if that made a difference. It still doesn't seem to be sensing any supply from the grid.

[Dave Foster]

If it showed ‘Normal’ that means it has found grid supply to be present and is operational ‘normally’ - the errors will stay showing for a while but are time stamped so may be old errors.

If the inverter has started up ok and is showing ‘normal’ you are back on-line but i’m wondering if your batteries are off-line in which case you need to shut down the whole system including the batteries and the restart by powering the batteries on first.

The small toroidal device you mention is the inverters CT clamp and that measures the power flow at the meter, it is an essential piece of equipment without that being connected properly the inverter cannot work out how much load is present and so the batteries won’t be used.

[StevePre]

Thanks Dave - now, this is intriguing.

Each time I previously powered down the system and brought it back up, I did as you suggested. Isolate DC > Isolate AC > turn off battery. Wait a bit, and then power-up in reverse order ie battery first, AC, then DC.

The inverter said that operation was normal but it wasn't detecting (or showing) flow to/from mains grid. What it was showing as 'load', included power going back to the grid (ie excess solar) but it didn't show that as export.

Perplexing. Could it be a sensor or sensor connection error?

[Dave Foster]

Thanks Dave - now, this is intriguing.

Each time I previously powered down the system and brought it back up, I did as you suggested. Isolate DC > Isolate AC > turn off battery. Wait a bit, and then power-up in reverse order ie battery first, AC, then DC.

The inverter said that operation was normal but it wasn't detecting (or showing) flow to/from mains grid. What it was showing as 'load', included power going back to the grid (ie excess solar) but it didn't show that as export.

Perplexing. Could it be a sensor or sensor connection error?

It sounds like your CT clamp has a connection problem - that wago connector in the photo was not designed to splice such thin wire - try re-making that.

Also check that the inverter thinks there is a CT clamp installed from the panel go to Settings, password (enter 4 times for 0000), Feature, Meter/CT, Set - it should say >CT< if it doesn’t use the arrow keys to select >CT< then press set. If it does say CT just exit the menu by pressing the far right button.

[StevePre]

Thank you

I'll give it a go and let you know.