Oso water heater shows E10 and will not start heating; often associated with external control signals.

Safety first: Turn OFF power before adjusting any control wiring. Only qualified personnel should modify BMS or external control circuits.

• Review wiring diagram: Refer to the Oso wiring schematic on the cylinder or in the manual. Confirm that external thermostat, timer, or BMS connections are on the correct terminals.
• Check external controls: Ensure any room thermostat, cylinder thermostat, or time switch calling the Oso heater is actually demanding heat (contacts closed).
• Inspect for shorts: Look for stray strands of wire bridging adjacent terminals on the control strip. Correct and re‑terminate as needed.
• Control mode settings: Some Oso models allow selection between local and external control. Verify the DIP switches or menu settings match the installation design.
• Bypass test (temporary): With power off, temporarily link the demand terminals as per the manual to simulate a call for heat. Restore power and see if E10 clears. Remove the link after testing.

If the heater works with a bypass but not with the building controls, the issue lies in the external wiring or devices, not the heater.