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A flame sensor proves there is a flame when your unit turns on. If the sensor detects no flame signal, the system shuts the gas off for safety. It protects your home by preventing unburned gas from flowing.
Specifications
- Part number: 100113151
- Brand: Ao Smith Water Heater
- Part type: Flame sensor
- Height: 1.9 in / 4.83 cm
- Length: 9.8 in / 24.89 cm
- Width: 9 in / 22.86 cm
- Rod length: about the same as your old one
- Mount: same bracket and screw spacing
- Connector: same terminal style
From the maker's and parts sellers' listings for this number. Compare them with the label on your old part.
What this flame sensor does
The flame sensor sits directly in the path of the burner flame. When the burner lights, the metal rod senses the heat and electrical current created by the fire.
This signal tells the control system that it is safe to keep the gas flowing. If the burners light, then go out after 3 to 10 seconds, a dirty or failing flame sensor is a common cause. Without a clear signal, the system stops the gas flow to keep the area safe.
Dimensions and measurements
When checking your old part against this number, verify the outer measurements. Use these exact specs to confirm the size of the part body and rod assembly.
- Height: 1.9 in / 4.83 cm
- Length: 9.8 in / 24.89 cm
- Width: 9 in / 22.86 cm
How to confirm a match
Matching a flame sensor requires comparing physical shapes and mounting features. Even small differences can keep the sensor from sitting properly in the flame.
- Rod length: about the same as your old one
- Mount: same bracket and screw spacing
- Connector: same terminal style
Checking for wear and replacing safely
Before replacing the part, inspect it closely. A light cleaning fixes many sensors. However, you should replace the part if the metal rod is bent or worn, or if the white porcelain insulator is cracked.
If you decide to replace it, follow safe installation habits to protect yourself and your equipment.
- Turn off electrical power to the unit at the breaker.
- Shut off the gas supply valve to the water heater.
- Take a photo of the wire connected to the sensor terminal before removing it.
- Remove the mounting screw, disconnect the wire, and pull the old sensor free.
- Mount the new sensor in place, secure the screw, and attach the wire to the matching terminal.
Read your old part
- Find the stamped or printed part number on your old sensor or its mounting bracket.
- Confirm the number reads 100113151.
- Compare the bracket shape and mounting screw hole spacing to your existing unit.
- Verify the rod length is about the same as your old sensor.
- Check that the electrical wire terminal matches the connector on your wiring harness.
When to call a pro
Hire a licensed HVAC technician for any step you are not sure you can do safely. If you smell gas or need gas valve work, stop immediately and call a licensed professional.
Questions
What causes the burners to light and then shut off after a few seconds?
If the burners light, then go out after 3 to 10 seconds, a dirty flame sensor is a common cause. When the sensor fails to confirm a flame, the control system cuts the gas supply for safety.
Can I clean my old flame sensor instead of replacing it?
A light cleaning fixes many sensors. You should replace the sensor if the rod is bent or worn, or if the white porcelain is cracked.
Can I bypass the flame sensor to keep the water heater running?
Never bypass a flame sensor. It is an active safety device designed to stop raw gas from building up inside your appliance.
What should I do if I smell gas while checking the sensor?
Do not touch any electrical switch. Leave the house immediately and call your gas company from outside.
Related part numbers
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Brand names and part numbers identify the part and show fit. HVAC Fitter is not affiliated with, authorized by, or endorsed by any equipment maker. If you are not sure a repair is safe for you, call a licensed HVAC technician.