E12
Oso
Partial Heating Element Failure / Phase Loss (Multi-element models)
Oso water heater shows E12; unit may still heat but with limited performance.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
One of multiple elements failed open, Loose connection on one element leg, Tripped internal thermal fuse on element, Burned contactor or relay for one stage
How to Fix / Troubleshooting
Safety first: Turn OFF power at the breaker and verify isolation before opening any electrical covers.
- Identify multi‑element configuration: Check the rating plate and wiring diagram to see how many elements or stages your Oso heater uses.
- Test each element: Disconnect wiring from each element and measure resistance across its terminals. Compare to expected values. Replace any element that is open or shorted.
- Inspect relays/contactors: On models with staged heating, check the control relays or contactors for burned contacts or loose spade connectors. Replace defective components.
- Tighten connections: Ensure all element terminal screws are tight and free of overheating signs.
- Reset and test: After repairs, restore power and confirm that all stages energize correctly and E12 clears.
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Repair Difficulty
Hard
4/5
Required Part
Oso immersion heating element assembly
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