Boiler shows E18 and may continue to run at reduced output

Safety first: Turn off power and gas. Gas valve work must be done carefully to avoid leaks.

• Inspect modulation wiring: Locate the modulation connector on the gas valve of the Utica boiler. Ensure the plug is fully seated and wires are intact.
• Check for wrong part: Verify that the installed gas valve matches the Utica model and gas type (natural or LP). An incorrect valve can cause modulation errors.
• Reset and observe: Restore power and gas, reset the boiler, and observe operation. If the boiler only runs at one firing rate or E18 recurs, further testing with a manometer and combustion analyzer is required.
• Professional service: Modulation and gas valve replacement should be performed by a licensed technician following Utica's combustion setup procedure.