Victron MultiPlus-II 24/3000 randomly dropping to passthrough — anyone else seen this?

Been having a frustrating issue with my MultiPlus-II 24/3000 installed in the shepherd's hut. About three weeks in, it started occasionally dropping out of inverter mode and going straight to passthrough when the grid hookup is connected — no fault codes, no alarms, just silently stops inverting. The only way I've noticed is the hut loads suddenly drawing from shore power rather than the battery bank.

Setup is 24V, 200Ah of Fogstar Drift LiFePO4 in 2S configuration, feeding through a 63A Victron SmartShunt before hitting the MultiPlus. Cerbo GX is on the system, and VRM shows nothing unusual at the moments it happens — battery SOC was at 87% when I caught it last time, so it's not an SOC-triggered handoff. Assistants running are ESS with grid setpoint at -50W, nothing exotic.

I've pulled the logs in VEConfig and the transfer switch activity tab shows the mode change but lists the reason as "internal" which is spectacularly unhelpful. Firmware is currently 497, which I believe is the latest stable. I've had a similar unit on my narrowboat for two years without a whisper of trouble, so this feels like it could be either a config oddity or possibly a marginal AC input quality issue from the site's hookup post.

Has anyone seen this "internal" reason code before, or found a way to get more granular logging out of the Cerbo? Wondering if it's worth temporarily tightening the AC input voltage window in VEConfig to rule out brief grid fluctuations triggering a quiet transfer.

@MarkBennett had the exact same gremlin in my shepherd's hut — turned out my AC input current limit in VE.Config was set too conservatively and the MultiPlus was essentially throwing a wobble every time the kettle kicked in, deciding shore power was "safer" and bailing on inverter mode like a coward.

Check your PowerAssist settings too — if it's enabled but misconfigured it'll flip to passthrough faster than you can say "why is my laptop dead."

Worth connecting via VE.Bus Smart Dongle and watching the live data when it trips; the assistant logs will basically tell you exactly what spooked it. Mine was embarrassingly simple once I could actually see the data rather than just staring at a blinking light feeling personally victimised.

Hey @MarkBennett, sorry to hear you're having this bother! Just to add to what @BatteryJason is getting at — worth also checking your DC input low shutdown voltage in VEConfigure. If your 24V bank is sagging under load even momentarily, the MultiPlus can interpret that as a low battery condition and flip to passthrough as a protective measure.

Also, have you got a BMV or SmartShunt fitted? Without accurate state-of-charge data, the unit might be making poor decisions about when to switch modes. What battery chemistry are you running — flooded, AGM, lithium? The charge profile settings matter a lot here.

Finally, check the transfer switch sensitivity setting — if you're on a noisy grid supply, it can sometimes confuse the unit. Grab the VEConfigure logs if you can, they'll tell you exactly what triggered each dropout.

Hey @MarkBennett, one thing worth checking that nobody's mentioned yet — have a look at your DC input low voltage thresholds in VE.Configure. If they're set too conservatively for a 24V system, the MultiPlus can decide to hand off to passthrough as a protective measure even when your batteries aren't actually in trouble. I've seen this catch people out, especially on shepherd's huts where the battery bank is sometimes on the smaller side.

Also, is your firmware fully up to date? There were a few quirks in earlier versions around the transfer switch logic that Victron quietly ironed out. Connect via VictronConnect and check — it's a two-minute job. What battery chemistry are you running? That might help narrow things down further.

@MarkBennett this is relevant to me too — I run a MultiPlus-II on my boat and had something similar. One thing nobody's flagged yet: check your AC input voltage range in VE.Config. If the lower threshold is set too conservatively (say, above 207V), the unit will flip to passthrough the moment shore power dips even slightly. UK grid can wobble quite a bit, especially on marina pontoons.

Also worth pulling the VRM logs if you've got a Cerbo or CCGX connected — the event history usually pinpoints exactly what triggered the switchover. Saved me hours of guesswork diagnosing my setup.

@MarkBennett had almost identical behaviour on my 48/5000 last summer. Turned out to be the AC input current limit set too low in VE.Configure — the unit was seeing the grid as insufficient and bailing out to passthrough as a protective measure rather than any fault condition.

Worth downloading VEConfigure 3 if you haven't already and checking the AC Input tab. Mine was set at 16A but the site supply had enough wobble on it that the MultiPlus was getting twitchy.

Also double-check your transfer switch settings — specifically the UPS function toggle. Sometimes flipping that off and back on has resolved ghost-switching issues people have reported on the Victron Community forums.

What firmware are you on? There were some known transfer relay quirks in older builds.

Really interesting thread — I've been lurking because I've got a MultiPlus-II on a narrowboat and want to avoid this exact issue.

One thing nobody's touched on yet: have you checked your VE.Bus System Configurator settings for the UPS function? If that's enabled, the unit can be quite aggressive about switching to passthrough when it detects any instability, even minor fluctuations. I had weird behaviour on mine until I tweaked that setting via VEConfigure.

Also worth asking — what's your shore power source? On a boat I've noticed that generators and hookup pedestals can both produce slightly dirty AC that the MultiPlus doesn't love. Could be similar on a hut hookup depending on cable length and supply quality.