A.O. Smith FPS 75 Technical Information page 19

FPS/FPSE/FPD TECHNICAL TRAINING AND SERVICE WORKBOOK
AIR FOR COMBUSTION
cont.
CONDITION CAUSE SOLUTION
Free air damper Excessive heat
build-up in PVC
venting
Inlet air damper not
opening completely
Blower does not run when
main burner fires
Replace entire
blower assembly
Wrong main burner
orifice size
Install correct
orifice
Intermittent
fan cycling
without burner
operation
(Propane Only)
Build up of
pressure in the
main burner tube
between thermostat
gas valve and
solenoid qas valve
If cycling occurs
more than twice per hour,
see troubleshooting
procedures.
A malfunctioning vent damper may also cause excessive heat buildup in the PVC vent piping
unable to free the damper, replace the entire combustion control tee.
If
If blower does not run when the main burner fires, replace the control
box.
Also check burner orifice
for correct size.
Intermittent cycling of the fan, without main burner operation, indicates a build-up of pressure in the
main burner tube between the thermostatic gas valve and solenoid gas valve.