Boiler shows E9 and will not operate, often after a power event or wiring change

Safety first: Turn off power at the breaker and verify with a non-contact tester before touching any wiring.

• Step 1 – Inspect power connection: Remove the electrical junction box cover on the Rheem boiler. Verify that line (hot), neutral, and ground are connected according to the wiring diagram on the boiler.
• Step 2 – Check polarity: Use a multimeter or outlet tester at the supply receptacle or disconnect to confirm correct hot/neutral orientation and presence of a proper ground.
• Step 3 – Verify voltage: Measure supply voltage to ensure it matches the boiler’s rating (e.g., 120 VAC ±10%). Overvoltage or undervoltage can trigger E9.
• Step 4 – Correct wiring issues: If line and neutral are reversed or ground is missing, correct the wiring at the source. Tighten all connections securely.
• Step 5 – Reset boiler: After correcting wiring, restore power and reset the boiler. If E9 persists with verified correct wiring, the main control PCB may have been damaged and require replacement.

Warning: Electrical work must comply with local electrical codes. If you are not comfortable working with live circuits, hire a licensed electrician.