Safety first: Turn off power and allow the system to cool. Depressurize if removing the sensor.

Step 1 – Compare readings: Compare the boiler’s digital pressure reading with the mechanical gauge (if present). A large discrepancy indicates a sensor or gauge issue.
Step 2 – Inspect sensor: Locate the system pressure sensor on the boiler’s hydraulic block. Check for leaks, corrosion, or damaged wiring. Reseat the connector.
Step 3 – Clean port: If accessible, remove the sensor and inspect the port for sludge or debris. Clean carefully and reinstall with appropriate sealing.
Step 4 – Replace sensor: If readings remain incorrect or E18 persists, replace the pressure sensor with the correct Rheem part.
Step 5 – Refill and bleed: After sensor replacement, refill the system to the correct pressure and bleed air.

Warning: Do not overpressurize the system to try to clear sensor errors. This can open the relief valve and cause water damage.

Boiler displays E18 and may show incorrect system pressure or lock out on pressure error

Possible Causes