Boiler shows E1 and will not fire, circulator may run briefly

Safety first: Turn off power and allow boiler to cool before opening any valves. Hot water and steam can cause severe burns.

• Check system pressure: Look at the boiler pressure gauge. For most Pennco hot water boilers, cold pressure should be around 12–15 psi in a typical two-story home. If below 10 psi, the boiler may lock out.
• Restore pressure: Open the manual feed valve or verify the automatic fill valve (pressure reducing valve) is supplying water. Slowly raise pressure to the recommended range while monitoring for leaks.
• Bleed air: Air pockets can trigger low water faults. Bleed air from radiators or baseboards and any automatic air vents near the boiler.
• Inspect LWCO sensor: Locate the low water cutoff probe or float assembly on the boiler. Check wiring connections for corrosion or looseness. Clean probe if accessible and fouled with scale (follow manufacturer instructions).
• If E1 persists with proper pressure: The LWCO or the integrated control board may be defective. Replacement of the LWCO assembly or control board should be done by a licensed technician.