Cerbo GX don't start

Had this exact grief on the narrowboat last summer — moved the whole Victron stack to a better cabinet and the Cerbo GX just sat there like a sulking teenager refusing to get out of bed.

Turned out the little swine had a dodgy connection on the VE.Direct cable that only revealed itself once everything got unplugged and replugged during the move. Three years of vibration had made the connector just barely acceptable, and the one unplug it took to shift things killed it stone dead.

Few things worth checking in no particular order:

• Power input — the Cerbo wants 8–70V DC on its dedicated supply, double-check it's actually getting juice and not just "probably getting juice"
• VE.Can termination resistors — if you've got a chain running, both ends need a 120Ω terminator or it'll throw a wobbler
• The fuse on the power lead — embarrassingly easy to overlook after a move
• Firmware — unlikely the culprit if it won't even boot, but worth knowing if you get it partially alive

Also worth trying a hard reset by pulling power for a full minute rather than just a quick flick — apparently the capacitors on these hold enough charge to confuse the boot sequence if you're too hasty.

Anyone else found the Cerbo particularly sensitive after a physical relocation? Feels like mine needs a two-week settling-in period every time I so much as look at it wrong. 🤔

What does yours do — any LEDs flash at all, or completely dead?

@FormerMechanic43 — classic one this. The Cerbo wants 8V minimum on the supply line before it'll even think about booting, but the real killer is voltage drop across undersized cable runs. Moved mine on the narrowboat last year and had identical grief — measured 12.4V at the battery, only 11.6V at the Cerbo connector under brief load. That's enough to trigger undervoltage lockout.

Check these in order:

1. Cable gauge — Victron recommend minimum 1.5mm² but honestly run 2.5mm² for any run over 30cm
2. Crimps and ferrules — corroded or loose connections are the silent killer in damp boat environments
3. The inline fuse holder — cheapo blade fuse holders develop serious resistance over time

Worth sticking a multimeter directly on the Cerbo's power terminals whilst pressing the button. If you're seeing anything below 10V there, your answer's in the wiring, not the unit itself.

@FormerMechanic43 had similar with my garden office build last year — everything looked wired right but the Cerbo just wouldn't wake up.

Ended up being a dodgy inline fuse holder causing a voltage drop. Looked fine visually but was dropping nearly 2V under load. Swapped it for a proper blade fuse block and it booted first time.

Worth checking:

• fuse holder quality — cheap ones are notorious for this
• cable connections at both ends, not just the Cerbo terminals
• run a multimeter directly at the Cerbo supply pins rather than at the battery

Don't trust your eyes on this one, measure everything.

@FormerMechanic43 worth checking your VE.Direct and VE.Can cables too — I've seen a dodgy data cable actually drag the supply voltage down just enough to confuse the Cerbo during boot. Pulled my hair out for a good afternoon on our 57-footer before I isolated that one. Also, if you've got a fused spur feeding it, double-check the fuse holder itself isn't corroded — on a narrowboat with all that condensation it happens more than you'd think. A fuse that reads fine with a meter can still have enough resistance under load to cause grief. Swap it out for a blade fuse inline holder if you haven't already, they're far more reliable in damp environments. Have you checked what the voltage is actually measuring at the Cerbo's terminals rather than back at the bus bar?

Good shout from @BoatClive on the data cables — I'd add that the power connector on the Cerbo itself is worth inspecting closely. Mine looked seated fine but one of the pins hadn't fully clicked into the housing after I'd disturbed things during a rewire on the garden office. Tiny movement, massive headache.

Also worth measuring voltage at the Cerbo's terminals rather than at the battery — I had an unexpected drop across a blade fuse holder that was corroding internally. Looked perfect externally, measured 0.8V drop under load. Swap your fuse holder if it's been in a damp environment (narrowboat especially).

Victron's own wiring guide specifies 0.75mm² minimum, 1mm² preferred for that supply line — undersized cable causes exactly this intermittent sulking behaviour under any kind of load spike.

Good points all round. One thing nobody's mentioned yet — the Cerbo's power input fuse on the harness itself. It's a blade fuse tucked into the supplied cable assembly and it's tiny enough to overlook completely during a reinstall. Caught me out on my shepherd's hut build; everything looked correct, 12V present at the supply end, but the inline fuse had blown silently at some point during handling.

Worth doing a proper voltage measurement directly at the Cerbo's power connector pins rather than upstream — that'll rule out fuse or cable resistance issues in one step. My Fluke confirmed 12.7V at the battery and precisely 0V at the unit. Mystery solved in about 30 seconds once I actually measured where it mattered.

Also confirm you're above the 7V minimum input threshold — a partially discharged bank during reinstall can catch you out.