Boiler displays E7 and may run at reduced output or lock out

Safety first: Turn off power before working inside the boiler cabinet.

Steps:

• Locate return sensor: Identify the return water temperature sensor on the return piping or lower section of the heat exchanger.
• Inspect connections: Ensure the sensor is firmly clamped to the pipe or inserted in the well and that the wiring is intact.
• Test sensor: Disconnect and measure resistance with a multimeter. Compare to Peerless spec chart. Replace if out of range.
• Check for swapped sensors: On some installations, supply and return sensors may be accidentally swapped. Verify wiring per the Peerless wiring diagram.
• If unresolved: A technician should verify sensor circuits at the control board and replace the return sensor or control as needed.