Heater is leaking water from the bottom of the cabinet.

Safety: Turn off power and gas. Shut off water flow to the heater by turning off the pool pump and closing isolation valves if present.

Steps:

• Identify fluid type: Feel and smell the liquid. Clear, cool water near the condensate drain on condensing models may be normal condensate. Warm, chlorinated water from the manifold area indicates a leak.
• Inspect unions and fittings: Remove the front and side panels. Check inlet and outlet unions for drips. Tighten slightly if loose, but do not overtighten plastic fittings.
• Check header gaskets: Look for water seeping from the joint between the heat exchanger and the inlet/outlet headers. Staining or corrosion trails indicate gasket failure.
• Examine heat exchanger: If water appears inside the combustion chamber or around the burner tray, the heat exchanger may be cracked.

Header gasket or heat exchanger replacement is complex and should be performed by a Lochinvar-trained technician.