Multiplus 2: flashing "mains on"

Running a Multiplus-II 48/3000 in my static caravan setup, connected to a Fogstar 48V LiFePO4 bank. Currently configured in ESS mode with grid tied to AC-in, but nothing on AC-out yet whilst I finish the wiring.

Everything seems to be behaving — charging looks correct, VRM is reporting sensible figures — but I've noticed the "mains on" LED is flashing intermittently rather than holding steady. It's not a rapid flash, more of an occasional blip, then solid again for a while.

A few questions:

• Is this normal behaviour in ESS when the inverter is essentially idling with no AC-out load?
• Could it be related to my grid supply quality? I'm on a rural single-phase supply that I know isn't the cleanest — occasional voltage dips
• Does the Multiplus-II use the flashing LED to indicate it's actively switching between grid and inverter (i.e., is it doing micro power-cuts to the AC-in side for some reason)?

I've had a look through the Victron ESS design guide but couldn't find anything specifically about LED behaviour in a no-load state. VEConfigure doesn't show any obvious alarms and the CCGX isn't flagging any faults.

Worth noting: I've not yet set the grid code properly — currently on the generic setting rather than UK G98/G99. Could that cause odd switching behaviour that shows up as a flashing LED?

Has anyone seen this with a similar setup, particularly on a rural supply? Should I be concerned or is this essentially cosmetic whilst there's nothing on AC-out?

@WattKaren the flashing "mains on" light usually means the Multiplus is detecting grid on AC-in but hasn't fully synchronised yet, or the grid quality is falling outside the accepted voltage/frequency window.

A few things worth checking:

• What's your AC input voltage range set to in VEConfigure? Default is quite tight (207-244V), and some caravan site hookups can be marginal
• Is your grid code set correctly for the UK? Should be on G98 or G99 depending on your setup
• Check the ESS assistant is actually loaded — if it's missing or misconfigured the unit gets confused about what it's supposed to do with AC-in

On my boat I had similar behaviour after a firmware update, turned out VEConfigure had reset a few parameters. Worth pulling the logs from VRM if you've got it connected.

@DaiYoung56 makes a good point about sync. One thing worth checking — have you gone through the AC input current limit settings in VEConfigure? I had a similar head-scratcher with my garden office setup (also Multiplus-II 48/3000) where the unit was seeing grid but the input limit was set so low it was essentially rejecting it.

Also worth confirming your grid code is set correctly for the UK — should be G98 or G99 depending on your DNO requirements. Wrong grid code can cause exactly this kind of limbo state where it detects mains but won't commit to it.

What does VRM or VictronConnect show for grid voltage and frequency on AC-in? If it's reading something daft like 0Hz that'd narrow it down quickly.

Also worth checking your grid code settings in VE.Configure — if you're on the wrong country profile (seen people accidentally left on "Other" instead of G98/G99) the Multiplus gets a bit suspicious of its own AC-in and just sits there flashing like it's having an existential crisis. Had a similar faff setting up ESS on my narrowboat before I realised I'd never properly committed the settings after making changes — VE.Configure will look like it saved but always double-check with a fresh readback. Also, is your Cerbo/Venus GX talking to it properly? ESS mode really wants that communication solid before it'll settle down and behave itself.

@WattKaren one thing nobody's mentioned yet — with ESS mode and nothing on AC-out, the Multiplus can sometimes behave oddly during initial commissioning because it's essentially waiting to "do something" with the grid connection. Worth double-checking in VE.Configure that your ESS assistant is actually installed and configured properly, not just that ESS mode is selected. Also, what's your Fogstar bank showing for state of charge? If the BMS is reporting below a certain threshold, the unit can hold off on completing synchronisation until it's happy the battery can support the transition. What does VEConnect show under the hub diagnostics? That'll give you a clearer picture than just the front panel LEDs.