Boiler attempts to start but shuts down with “Err 3” before ignition, fan or circulator may run briefly

Safety first: Shut off power before working on wiring or controls. Hot water can scald; open vents slowly.

• Check system pressure: Read the boiler pressure gauge. For most Burnham hot water boilers, cold pressure should be around 12 psi (two-story home) and higher for taller buildings. If pressure is near zero, the LWCO will prevent firing.
• Verify automatic fill: Locate the pressure reducing valve (auto-fill) on the cold water feed line. Ensure the manual shutoff valve ahead of it is open. If pressure does not rise when you lift the fast-fill lever, the valve may be clogged or failed.
• Inspect LWCO: Identify the low water cutoff (probe-type or float-type). Check wiring connections for corrosion or loose terminals. For probe types, mineral buildup can cause false low-water readings.
• Manually add water (if safe and allowed): If you are familiar with your system and local codes permit, you can slowly open the manual feed valve to raise pressure to 12–15 psi while bleeding air from high points. Do not overfill above 25–28 psi.
• Reset LWCO: Some LWCOs have a manual reset button. After restoring proper pressure, press and hold the reset once. If the boiler fires and runs normally, monitor for leaks that may be causing pressure loss.
• Call a professional if: Pressure will not hold, the LWCO continues to trip, or you see water leaks from relief valves, radiators, or boiler sections.