Air Pressure Switch Operation - State Water Heaters GP650 HTPDT Service Handbook

Ultra high efficiency power vent / power direct vent commercial/ residential gas water heaters
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ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL

AIR PRESSURE SWITCH OPERATION

The control system monitors the "state" of the air pressure switches individually through
three separate circuits (see wiring on diagram page 39). The "state" of the switch refers to
whether the switch contacts are open or closed. See the construction drawings on page 18.
Before each call for heat begins, before the blower starts, the control system performs a
diagnostic test. During this test the control system checks the air pressure switches. The
switches must be in their correct normal state at this point.
The Blower Prover is a normally open switch and the Blocked Intake/Exhaust switches are
normally closed. If the Blower Prover is not verified open or the Blocked Intake/Exhaust
switches are not verified closed during this test; the control system would lock out and
display a fault message indicating which pressure switch had caused the fault condition. IE:
"Blower Prover Failure."
After the blower starts the Blower Prover switch contacts must activate (close) for the
water heater to continue in the Sequence of Operation (see page 40). If the Blower Prover
switch contacts do not close after the blower starts, the control system would lock out and
display a fault message; IE: "Blower Prover Open."
Normal State
Activated State
Blower Prover
(contacts open - before blower starts)
Air Pressure Switch
(contacts closed - after blower starts)
Normally open contacts,
close on a rise in pressure.
The Blocked Intake and Blocked Exhaust switches must remain closed at all times. If the
control system senses the contacts of either of these switches are open it will lock out and
display a fault message; IE "Blocked Inlet" or "Blocked Exhaust Vent"
Technical Literature Department
20 of 52
Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent

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