Safety first: Turn off power before accessing internal wiring or sensors.

Step 1 – Locate flow sensor: Find the flow (supply) temperature sensor on the boiler’s outlet pipe. It is usually a small probe or clip-on sensor with two wires.
Step 2 – Inspect wiring: Check the sensor harness for cuts, abrasions, or pulled connectors. Reseat the connector at both the sensor and main PCB.
Step 3 – Check for moisture: Look for signs of water leaks dripping onto the sensor or wiring. Repair any leaks and dry the area thoroughly.
Step 4 – Measure resistance: With power off, disconnect the sensor and measure its resistance with a multimeter. Compare to Rheem’s temperature/resistance chart at the current water temperature. Replace the sensor if readings are out of range or unstable.
Step 5 – Inspect harness to PCB: If the sensor tests good, the wiring between the sensor and PCB may be shorted or open. Repair or replace the harness as needed.

Warning: Do not operate the boiler with a bypassed or incorrect temperature sensor. Overheating and damage can occur.

Boiler displays E10 and will not start, often after sensor wiring work

Possible Causes