Anyone else running Victron Cerbo GX on a narrowboat and finding the tank level sensors absolutely useless?

Mine reads "87% full" while I'm clearly running on fumes — genuinely considered whether the boat was haunted before I remembered I'd bought a cheap sender from eBay.

Running a Fogstar 200Ah lithium bank with a SmartShunt doing all the actual honest work, so at least my battery monitoring is sorted. The Cerbo dashboard looks gorgeous though, I'll give it that — like a lying ex who presents very well.

Has anyone found a decent tank level sender that actually plays nicely with the Cerbo's 0–180Ω input without needing a degree in electrical engineering to calibrate? Or am I doomed to just knocking on the tank and listening like it's 1987?

JackieEdwards75 | 847 posts | ⚡ Solar Evangelist

@OffGridJulie Ha, the haunted boat theory is genuinely more comforting than admitting you've been had by a £4 eBay sender! 😄

The Cerbo's tank monitoring is only as good as what you feed it — it expects a 0-180 ohm resistive sender typically, and half the cheap ones floating around are wired for American spec (240-33 ohm). Completely backwards readings.

Worth measuring your sender's actual resistance range with a multimeter at empty and full, then you can manually configure the input range in VictronConnect under the tank settings. Took me an afternoon to sort mine on Bramble and it's been spot-on since.

If it's genuinely a duff sender, Wema do decent quality ones that play nicely with Victron kit without costing a fortune. Proper UK spec too.

DevonCruiser | 312 posts | 🔋 Lithium Convert

@OffGridJulie The sender resistance range is almost certainly your culprit. Victron's tank monitoring expects a specific ohm range (typically 0-180Ω or 10-180Ω depending on configuration) and cheap eBay senders often output something completely different — hence the phantom readings.

Worth checking in the Cerbo GX settings under Tank Level Sensors — you can manually adjust the empty/full resistance values to match whatever your sender actually outputs. Bit fiddly but it sorts it properly.

If the sender itself is dodgy though, honestly just replace it with a proper Wema or Faria unit. Costs a tenner or so more but calibrates reliably and the Cerbo plays nicely with them.

What's your current empty/full resistance showing in VRM when you check? That'll tell you straight away whether it's a configuration issue or a dead sender.

IvyDai | 203 posts | 🚤 Liveaboard

@OffGridJulie Been there! The Cerbo expects a specific resistance range for tank sensors — typically 0-180 ohms or 10-180 ohms depending on your configuration in the VRM portal. Most cheap eBay senders are wired for automotive applications using completely different ranges, so the readings are essentially meaningless.

Worth checking your tank sensor settings under Device List → Tank on the Cerbo touchscreen and matching the sender spec properly. Wema or Garnet are the go-to brands for marine use that actually play nicely with Victron. Also double-check you've selected the correct fluid type — I accidentally had mine set to "Blackwater" for my diesel tank for three months which didn't help anyone's morale! 😅

What sender resistance range does yours claim to be?

JennyThomas57 | 203 posts | ⛵ Afloat & Off-Grid

I went through exactly this saga on our narrowboat last spring. Turns out the Cerbo expects a specific resistance range — ours was wired to a sender that topped out at 180Ω when Victron wants 0-180Ω starting from the other end. Reading was inverted the entire time. Full looked empty, empty looked full.

Swapped to a proper Wema sender and configured the custom tank sensor curve in VRM. Takes about ten minutes once you've found the right menu buried in the Cerbo settings. Night and day difference.

Worth checking whether your sender is even the right physical type for your tank shape too — a flat tank reads completely differently to a cylindrical one if the float travel isn't calibrated for it.

Ben1968 | 87 posts | 🏕️ Static & Shepherds Hut

Not on a narrowboat myself but had nearly identical headaches with tank sensors on my static caravan setup. The Cerbo's tank inputs are dead fussy about sender range — if it's not matched properly you'll get ghost readings all day long.

Worth checking the Victron VRM portal — you can recalibrate the sensor range in there rather than replacing the whole sender. Set your custom min/max resistance values to match whatever the eBay unit actually outputs.

Failing that, @OffGridJulie a Wema or Mopeka sensor is worth the money for a proper match. Cheap senders are a false economy every time — learned that the hard way on my shepherd's hut water tank before I just bit the bullet on decent kit.

RustyCaptain | 341 posts | 🚤 Liveaboard

@OffGridJulie The "haunted boat" phase is a rite of passage, honestly! One thing worth checking that nobody's mentioned yet — the Cerbo's tank sensor input expects 0–180Ω (VDO standard), but a lot of cheap eBay senders output 10–190Ω or even 33–240Ω. Even a genuine sender wired with slightly too much resistance in the cable run can throw the readings completely sideways. I'd grab a multimeter and measure what your sender is actually outputting at empty and full before buying anything else. If you're handy with Node-RED on the Venus OS, you can also apply a custom calibration curve and essentially bodge mismatched senders into giving sensible readings. Saved me buying a replacement on Perseverance last autumn. What sender range does the eBay listing actually spec?

Moorey44 | 56 posts | 🚐 Motorhome

Not a narrowboat setup but running a Cerbo GX in my motorhome and the tank level situation is just as chaotic — had a Victron-compatible resistive sender that drifted wildly depending on water temperature apparently. Ended up fitting an ultrasonic sensor instead and the readings are rock solid now. Worth looking at the Mopeka units if you haven't already, they clip straight onto the outside of the tank so no sender rod to corrode or stick. Only downside is the Cerbo integration needs a BLE workaround but there are decent guides on the Victron Community forum for it.