Heater displays E30 and will not start; often associated with low-voltage issues.

Safety First: Turn off power at the breaker before opening the electrical compartment.

• Measure line voltage: With a multimeter and power restored, verify that the voltage at the heater's input terminals matches the nameplate rating. If low, correct the supply issue.
• Inspect connections: Tighten all line and neutral/ground lugs. Look for discoloration or melted insulation, which indicates overheating.
• Dedicated circuit: Ensure the heater is on a dedicated circuit sized according to Rheem's installation manual. Remove other loads if sharing is causing a voltage drop.
• Check internal transformer (if present): With power off, inspect the low-voltage transformer for overheating or buzzing. Replace with a Rheem-specified transformer if it is defective.