INTELLI-VENT TROUBLESHOOTING GUIDE
Technical Training Department
Ashland City, Tennessee © 2005
20 of 24
TECHNICAL BULLETIN - AIR PRESSURE SWITCHES
A-023-04 & S-024-04 COMBINED
Air pressure switches are used on all fan assisted gas fired water heaters, residential and
commercial. If the water heater was factory equipped with a combustion blower or inducer
fan, by design the blower must running during the heating cycle.
Air pressure switches are used to provide verification, or prove electrically, that the blower
is running and the vent and/or combustion air piping is not blocked or restricted.
The ignition control on these fan assisted boilers and water heaters senses when the “air
pressure switch circuit” is open or closed. There is at least one air pressure switch in this
circuit that has normally open contacts on all models (see page 5). As the blower starts and
comes up to speed the normally open contacts on this air pressure switch will close in
response to changes in vent system pressure.
At the beginning of a heating cycle the ignition control will check if the air pressure switch
circuit is open before the control energizes the blower motor.
The ignition control will check the air pressure switch circuit a second time to insure it is
closed after the blower is energized.
The ignition control then monitors this circuit during the heating cycle to insure the circuit
remains closed. If this circuit opens (even for a split second) during the heating cycle; the
control will close the gas valve immediately to insure safe operation.
In this way an ignition control can perform three critical diagnostic checks using a single air
pressure switch:
1 Verify the normally open air pressure switch contacts are not stuck closed or jumpered.
2 Verify the combustion blower or inducer fan is running.
3 Verify the vent and/or combustion air piping remain free of restrictions.
Pressure switch construction, operation, testing, the various types of pressure switches
and their wiring are explained in this bulletin.
Summary of Contents for INTELLI-VENT
Page 34: ......
Page 43: ...Intelli Vent Sequence of Operation...
Page 44: ......
Page 45: ......
Page 46: ......