Boiler will not fire and indicates 'Low Water', 'LWCO', or low water cutoff fault; gauge may show low or zero pressure.

Safety first: Never add water to a hot, dry boiler. Allow the boiler to cool. Steam boilers are especially dangerous if fired dry.

• 1. Check system pressure: Read the pressure gauge. For hot water Weil-McLain boilers, cold fill is typically 12–15 psi. If pressure is low, the system may need water.
• 2. Inspect automatic fill valve: Locate the pressure reducing valve (auto-fill). Ensure the manual shutoff valve feeding it is open. Lift the fast-fill lever briefly to see if water flows and pressure rises.
• 3. Check for leaks: Look for visible leaks at radiators, relief valve discharge, boiler piping, or under the boiler. Repair leaks before refilling.
• 4. Reset LWCO: Some low water cutoffs (probe or float type) have a manual reset button. After restoring proper water level/pressure, press reset.
• 5. Clean LWCO probe (if accessible): With power off and boiler drained to below the probe, remove the LWCO probe and clean mineral buildup with a Scotch-Brite pad. Reinstall with new gasket if required.

If the LWCO continues to trip, or if you are unsure how to safely restore water level, contact a professional.