Water Heater Blower Prover Switch 101

Erin Trybulec • Oct 20, 2020

Article Contributor | J. Trybulec + J. Richards + K. Warren


***DISCLAIMER: PLEASE REFER TO YOUR MANUFACTURER’S INSTALLATION MANUAL FOR INFORMATION REGARDING YOUR SPECIFIC MODEL. IF YOU ARE ATTEMPTING TO SERVICE YOUR OWN HEATER, PLEASE DO SO WITH CAUTION. THIS ARTICLE IS MEANT TO PROVIDE AN INFORMATIVE + EDUCATIONAL SUMMARY AND DOES NOT SUPERSEDE OFFICIAL ONSITE DIAGNOSIS/REPAIRS OR INFORMATION FROM THE UNIT’S MANUFACTURER.

What is a Blower Prover Switch?
A Blower Prover Switch is a switch/sensor that a water heater’s blower assembly relies on to sense air flow. If there is air flow, the blower prover switch stays open, signaling the blower that there is exhaust flow; the blower then allows the gas valve to operate. If the blower prover switch senses a lack of air flow and closes, the heater will shutdown as a safety mechanism to avoid the risk of exhaust becoming trapped indoors.

How does it sense airflow?
Blower Proves Switches have a small blue tube attached to them. The tube senses the airflow. If the tubing is kinked, filled with condensation, or damaged, it may cause the blower prover switch to close (thus communicating to the unit that it should shutdown).    

What are some common Blower Prover Switch issues?
+ Issue: During the Winter, it is extremely important to make sure that there is no snow or ice blocking the path of the exhaust. Condensation and cold airman also block the air flow of the exhaust. 
 + Result: Blower Prover Error
 + Solution: Ensure that there is no snow, ice, or blockage preventing you unit from expelling exhaust
   + Issue: Back pressure caused by rust in the condensate elbow (the condensate elbow fills up with rust, blocking exhaust airflow. 
   + Issue: Animals that crawl inside the exhaust and block airflow
 + Solution: Regular maintenance and ensuring the venting is not blocked
   + Issue: Flue Baffle is seated improperly and it trips the pressure switch
          + Solution: Flue Baffle needs to be secured down  

Are Blower Prover Switches expensive?
Blower Prover Switches typically cost between $45.00 to $150.00 depending on whether it is for a commercial or residential unit.

Do you stock Blower Prover Switches?
Yes. We stock a variety of Blower Prover Switches, especially for A.O. Smith commercial water heaters.
   + Common A.O. Smith part numbers we stock: 
+ 100113144
+ 100111056
+ 100109962
+ 100110806
+ 100110729
+ 100111021
+ Although many switches (but not all) come with the tubing, it can also be found as under its individual part number: 100111026.

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