Boiler shows E05, will not start, fan or pump may run but burner does not light

Safety: Turn off power. Do not add water to a very hot boiler; allow it to cool to avoid thermal shock.

Steps:

• 1. Check system pressure: Read the pressure gauge on the boiler. If below about 12 psi (typical for a 2-story home), the system may be underfilled.
• 2. Restore water pressure: Locate the automatic fill valve/pressure reducing valve. Ensure the manual shutoff to it is open. If your system uses manual filling, slowly open the feed valve and watch the gauge until it reaches the recommended cold pressure (usually 12–15 psi). Close the valve.
• 3. Reset low water cutoff: If your Slant/Fin boiler has an external LWCO, press the reset button once after pressure is restored. Do not repeatedly reset without correcting the cause.
• 4. Bleed air: Air pockets can cause false low-water readings. Bleed radiators and high points in the system until water flows steadily.
• 5. Inspect for leaks: Look for water around boiler piping, relief valve discharge, and radiators. Ongoing leaks must be repaired to prevent recurring low water faults.

Professional help: If E05 persists with correct pressure, the LWCO or pressure sensor may be defective and should be tested and replaced by a technician.