The short answer
Possibly reverse cables or MOSFET failure: power off, check cables, test one module alone, then contact the distributor.
Plain explanation
From the Pylontech manual for the US5000: Power off everything, disconnect breaker. Check cables and ports. The rest of the checklist is below; work through it in order. This is a warranty/support case: note the code, time and serial number before calling the manufacturer.
Steps from the source
- Power off everything, disconnect breaker
- Check cables and ports
- Turn on a single module without cables
- Distributor
Source
Pylontech US5000/US5000-B Installation Manual V1.0 (2024-09), Troubleshooting, Troubleshooting, printed p27-29pylonwebs3.s3.amazonaws.com ↗
Where installers ask this
- Can't connect US3000C battery to ME3000SP inverter (r/SolarDIY)
- reddit.com/r/SolarDIY/comments/x5xhsc/
- reddit.com/r/SolarUK/comments/1k51sqd/
General guidance based on the manufacturer's manual or the named source. Always follow the current manual for your exact model and your national code. DC and AC electrical work is for qualified installers only. Not affiliated with or endorsed by any brand named; trademarks belong to their owners.