Sudden grid ground relay test failue Error 11

Bit of a frustrating one this, and curious whether others have hit the same wall.

My setup is a pair of Victron Multiplus-II 48/3000s running in single-phase parallel — been solid for nearly three years in the tiny house without so much as a hiccup. Last week I started getting Error 11 on both units simultaneously, which is the ground relay test failure. Both units throwing it at the same time strongly suggests it's not a fault with either inverter individually, which is what's making this tricky to diagnose.

From what I understand, the ground relay test fires on startup and checks that the neutral-earth bond is behaving correctly. A few things I've been working through:

• Neutral-earth bonding — is something upstream creating a second N-E bond that's interfering? I checked my consumer unit and the Multiplus output wiring, and nothing obvious jumped out.
• Wiring degradation — damp ingress over winter is always a suspect in an off-grid install. I've pulled out the DB and visually inspected, but haven't done a full insulation resistance test yet.
• Firmware — both units are on the same firmware version, so I doubt that's the culprit, but worth mentioning.

The fact that it appeared suddenly after years of reliable operation makes me lean toward a physical wiring issue rather than a configuration problem. Has anyone seen moisture or a failing earth connection cause this specific error on parallel Multiplus units?

Would also be interested to know whether anyone has used the Victron diagnostic tools via VE.Bus to get more granular data on exactly when in the relay test sequence it's failing.

@KangooNomad had almost the exact same thing on the narrowboat last autumn — Multiplus-II 48/3000, woke up one morning to Error 11 out of nowhere after a perfectly normal night.

Turned out my neutral-to-earth link had developed a dodgy connection at the busbar. The relay test fires a brief connection and measures the response — if the N-E bond is loose or corroded, it sees an unexpected impedance and throws the fault.

Worth checking:

• The N-E bonding jumper on your AC input panel
• Any isolator switches in that circuit
• Run VictronConnect and pull the full diagnostic log — it'll show whether the test is failing consistently or intermittently

Mine was intermittent, which actually made it harder to chase down. Reseating and re-torquing every terminal on that neutral bar sorted it completely. Boats and damp environments make this worse, but cabins with ground temperature swings can do the same thing.

Really feel for you on this one — Error 11 has a bit of a reputation for being elusive.

When mine threw it on the static caravan setup, the culprit turned out to be the neutral-earth bond at the distribution board rather than anything inside the Multiplus itself. The relay tests that connection on startup, and even a slightly loose terminal was enough to cause intermittent failures.

Worth pulling the Ve.Configure software up and checking your ground relay test setting is actually enabled correctly — sometimes a firmware update quietly shifts that parameter. I'd also check whether both units in your parallel pair are running identical firmware versions, because a mismatch can cause exactly this kind of ghost fault.

If you haven't already, the Victron Community forum has a diagnostic flowchart specifically for Error 11 parallel configurations that's worth bookmarking.

Has the neutral-ground bonding been checked at the inverter itself? On my static caravan setup I chased Error 11 for about a week before realising the internal relay contact had developed high resistance — not fully open, just dirty enough to fail the test. Victron's own relay test threshold is fairly tight.

Worth pulling the unit and doing a resistance check across the relay contacts directly if you can. Also — are both Multiplus-II units throwing the error, or just one? If it's isolated to a single unit that points strongly toward a hardware fault rather than a wiring or configuration issue. Victron UK support can sometimes authorise a relay replacement without a full unit return if you've got a decent dealer relationship, so worth ringing your supplier before sending anything off.

Jumping in here as I've been lurking on Error 11 threads for a while — had a similar scare on my lithium setup recently.

One thing nobody's mentioned yet: have you checked whether the relay test is actually failing consistently or only on certain battery states? Mine was throwing it intermittently and turned out the DC bus voltage was dipping just enough during the relay test cycle to trigger it — BMS was briefly throttling output from my Fogstar cells.

Worth logging the battery voltage at the exact moment of failure through the VRM portal if you've got that set up. Victron's relay test runs at startup and is apparently quite sensitive to voltage fluctuations in that window.

Did you change anything on the battery side before this started — new BMS firmware, charge limits adjusted, anything like that?