Boiler displays E8 and will not fire; may indicate low water pressure or flow.

Safety first: Turn off power. Be cautious when adding water to a hot system; thermal shock can damage the boiler.

• Step 1 – Check pressure gauge: Read the boiler’s pressure gauge. For most residential systems, cold pressure should be around 12–20 psi. If it is below the minimum specified, the system needs to be filled.
• Step 2 – Verify fill valve operation: Locate the automatic fill (pressure reducing) valve. Ensure the manual shutoff valve feeding it is open. If pressure does not rise when the fast-fill lever is engaged (if equipped), the fill valve or house water supply may be restricted.
• Step 3 – Bleed air: Air pockets can trigger low-flow or low-pressure faults. Bleed air from radiators, baseboards, and automatic air vents. Top up system pressure as needed during bleeding.
• Step 4 – Inspect for leaks: Look for visible water leaks at boiler piping, relief valve discharge, circulator flanges, and radiators. Repair leaks before refilling to proper pressure.
• Step 5 – Check low water cutoff / pressure switch: If pressure is normal but E8 persists, the low water cutoff or pressure switch may be faulty. Inspect wiring and replace the device if it does not change state at the correct pressure (requires testing by a technician).

Note: Never bypass a low water cutoff; operating a boiler without adequate water can cause severe damage or explosion.