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This switch verifies that the draft inducer is running and venting properly before allowing the system to light. If venting issues arise, it keeps the unit from running.
Specifications
- Part number: 100217965
- Brand: A.O. Smith
- Part type: Pressure switch
- Height: 2 in / 5.08 cm
- Length: 6 in / 15.24 cm
- Width: 5.05 in / 12.83 cm
- Setpoint: same inches WC, like -0.90 in
- Contacts: same type, usually normally open
- Ports: same number of hose ports
From the maker's and parts sellers' listings for this number. Compare them with the label on your old part.
What this safety switch does
A pressure switch is designed to protect your home. It confirms that the draft inducer fan is operating and that exhaust gases can exit safely through the vent.
The switch allows ignition only when it senses that the venting path is completely clear. If it detects a blockage or a weak draft, it remains open and keeps the burners from lighting.
Dimensions and physical specs
When comparing your current switch to part 100217965, check the physical dimensions listed for this part number.
Physical size ensures the replacement fits properly into the existing mounting bracket inside the cabinet.
- Height: 2 in / 5.08 cm
- Length: 6 in / 15.24 cm
- Width: 5.05 in / 12.83 cm
Confirming the right match
Matching a pressure switch requires checking both the part label and the operating characteristics. Never install a switch with incorrect pressure ratings or terminal configurations.
- Setpoint: verify the same inches WC rating, such as -0.90 in, listed on your original part.
- Contacts: confirm the same contact type, which is usually normally open.
- Ports: verify the switch has the exact same number of hose ports as your old unit.
Troubleshooting and safe replacement
A pressure switch error does not always mean the switch itself is broken. External problems often cause the switch to trip.
Check the pressure tubing first. A cracked hose, a clogged drain, or a blocked vent pipe can make a properly functioning switch open. Clear those items before replacing parts.
If the switch must be swapped, follow these steps to complete the task safely.
- Shut off electrical power to the unit at the circuit breaker and confirm power is off with a tester.
- Take a clear photo of all wiring connections and tubing attached to the switch.
- Disconnect the small tubing, checking for moisture, cracks, or dirt inside the hose.
- Remove the mounting hardware and move each wire one at a time to the matching terminal on the new part.
- Secure the switch in place, reconnect the hose firmly, and restore power to test operation.
Read your old part
- Locate the label on your existing pressure switch.
- Check that the part number reads 100217965.
- Confirm the brand name on the equipment or part matches A.O. Smith.
- Compare the number of hose ports to be sure they match your existing tubing setup.
- Verify the contact style and pressure setpoint on the label match your old switch.
When to call a pro
If your pressure switch keeps tripping, if you suspect vent pipe blockages, or if you are not sure you can complete the repair safely, hire a licensed HVAC technician. If you ever smell gas, leave your home immediately and call your gas company from outside.
Questions
Can I bypass this pressure switch to see if the heat turns on?
Never bypass a pressure switch. It is a safety device designed to protect your household. Jumping the switch can allow dangerous carbon monoxide to enter your home.
Why is my pressure switch open if the switch is not broken?
A cracked hose, a blocked exhaust vent, or a backed-up drain line can keep the switch open. The switch is doing its job by stopping the burners when airflow is unsafe. Inspect hoses and vents before deciding the part has failed.
What should I do before disconnecting the wires?
Always turn off power at the breaker panel and test for power before touching wiring. Take a photo of the connections so you can transfer the wires one at a time to the exact same spots.
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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.