A.o. Smith 100109721 Upper Probe Hot Surface Igniter

Product Description

The A.O. SMITH 100109721 is a hot surface igniter serving as the upper probe for the inner control assembly on commercial water heaters. It initiates combustion by generating the heat needed to light the burner on natural gas and propane-fired units. This igniter is a direct-replacement component for licensed plumbers and HVAC technicians servicing A.O. SMITH commercial water heater lines. Proper igniter function is critical to reliable system startup, and a failed or cracked igniter is a common cause of no-heat or lockout conditions on standing-pilot-free systems.

This igniter is designed for use in commercial water heater applications running on natural gas or propane. It is specified for A.O. SMITH BTH, SUF, and HCG series units across a range of sizes including the 60-120, 100-150, 100-199, and 100-250 models. These are high-input commercial water heaters typically found in multifamily residential buildings, light commercial facilities, and institutional settings. Installation is performed by licensed plumbers or gas service technicians during routine maintenance or burner assembly service calls.

Key Features

• Functions as the upper probe within the inner control assembly for reliable ignition sequencing
• Compatible with both natural gas and propane fuel types
• High-efficiency design suited for commercial-grade water heating systems
• Direct OEM replacement for BTH, SUF, and HCG series A.O. SMITH units
• Addresses common ignition failure and burner lockout conditions

Compatibility

Designed for use with A.O. SMITH BTH, SUF, and HCG series commercial water heaters, including models 60-120, 100-150, 100-199, and 100-250, on natural gas and propane systems.

Installation Notes

Installation should be performed by a licensed plumber or gas service technician in accordance with local codes and the IFGC. Shut off the gas supply and disconnect power to the unit before removing the burner access panel or handling the igniter assembly. Hot surface igniters are fragile — avoid contact with bare skin, as oils can cause premature failure. Verify igniter resistance and circuit continuity with a multimeter before completing reassembly.

Technical Specifications

• Application: Heating
• Fuel Type: Natural Gas, Propane
• Component Role: Upper Probe, Inner Control Assembly
• Compatible Series: BTH, SUF, HCG
• Compatible Size Range: 60-120, 100-150, 100-199, 100-250

Standard Information

• Brand: A.O. SMITH
• Manufacturer Part Number: 100109721