Blower Prover - A.O. Smith 100 Series Service Handbook

DISPLAYED MESSAGE/CONDITION/INDICATES

Blower Prover

Combustion Blower IS NOT Running
(If the Combustion Blower is running see "Blower Prover - Combustion
Blower Is Running" on the following page)
The Control System has not energized the Combustion
Blower or the Combustion Blower has failed to start when
energized.
Operational & Service Notes:
The BPS (Blower Prover Switch) is dual pressure sensing
switch. It is a normally open switch that closes its contacts
on a fall in pressure difference between the P1 and P2
pressure sensing ports on the switch. The activation
pressure for the switch to close its contacts is -4.0" W.C.
(inches water column). This activation pressure is a
negative pressure; a slight vacuum. See Control Panel on
page 17 for BPS location.
The Control System monitors the BPS during the
diagnostic system check at the beginning of each heating
sequence, before energizing the Combustion Blower, to
ensure the normally open switch contacts are open. If the
BPS circuit is closed for any reason, the Control System
will not energize the blower and will lock out and display
the "Blower Prover" Error Message on the UIM's LCD.
See the Sequence Of Operation on page 45.
The Control System also monitors the BPS during three
(3) operating states; pre-purge, inter-purge and post-
purge when the blower is running at high speed to ensure
the BPS switch contacts have closed to verify the blower
is operating at high speed.
During the Igniter Warm Up period and Heating Mode
operating states, when the blower is running at lower
speeds and will not achieve a -4.0" W.C manifold pressure,
the Control System is programmed to ignore the state of
the BPS switch contacts.
Important Service Reminder:
When performing any troubleshooting steps outlined in
this manual always consider the wiring and connectors
between components. Perform a close visual inspection
of all wiring and connectors to a given component before
replacing any electrical part or component.
Servicing should only be performed by a Qualified Service Agent
CHECK/REPAIR
Turn the boiler off for the following tests:
• Ensure there is not a jumper wire installed between
the two wiring terminals on the BPS (Blower Prover
Switch), see Figure 11 on page 18.
• Disconnect both wires from the BPS - check for
continuity between the two terminals on the switch
using an ohm meter. If there is continuity - replace
the switch.
• Check all wiring between the BPS and the J17
Socket on the MCB, see MCB - Section B on page
21. Ensure the wiring is not shorted/pinched - repair/
replace any shorted/damaged wiring.
• Check the plug/socket connections at the PDB J3
Socket and the 3 pin 120 VAC connector on the
Combustion Blower. Ensure the plug/socket pins are
in good condition and making good contact - repair/
replace anything worn or damaged, see Figure 4 on
page 10 and PDB - Section D on page 32.
• Check all wiring between the PDB J3 Socket and the
3 pin 120 VAC connector on the Combustion Blower -
repair/replace any wiring that is damaged or worn.
• Check the F7 fuse on the PDB - replace the fuse if
blown, see PDB - Section B on page 30.
The boiler is turned on with a call for heat active
during the following tests:
Perform the voltage tests below by inserting the meter
test probes into the back of the wiring harness plugs while
they are still inserted in their respective sockets.
• Disconnect the two wires to the BPS to ensure there
is an open BPS circuit and restart the boiler. The
Combustion Blower should start in this condition.
• Unplug the 5 pin connector on the Combustion
Blower and restart the boiler, see Figure 4 on
page 10. The Combustion Blower should start and
run at high speed continuously in this condition. If
the Combustion Blower does start call the toll free
support phone number on the back cover of this
manual for further assistance.
• Check for 120 VAC at the 3 pin 120 VAC power
supply plug on the Combustion Blower, see Figure 4
on page 10 and the wiring diagram that came with the
boiler.
• Check for 120 VAC between pins 1 and 2 of the J3
Socket on the PDB.
• Call the toll free support phone number on the back
cover of this manual for further assistance if the
problem has not been corrected after performing the
procedures outlined here.
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