Form I-RA/D 140/235 (Version A), Mfg No. 110318 Rev 4, Page 37
• Burning off-specification fuel
• Changes in outside ambient temperature
Location
- The backflow sensor switch is mounted on a bracket on
the hinged viewport cover on the control side of the heater. The lo-
cation is important in the operation of this switch. Except for limited
observation, the viewport cover must be kept closed for the sensor
(and heater) to operate properly.
Operation
- Underneath the sensor bracket, the viewport cover
has a 3/8” diameter hole. Under normal negative overfire operating
conditions, room air is constantly drawn into that small opening. The
temperature-sensitive backflow sensor is “cooled” by the air flow. If
for any of the reasons listed, the furnace pressure becomes zero, or
slightly positive, the flow of air decreases. If this condition persists
(10 minutes maximum) the “uncooled” backflow sensor activates
interrupting power to the ignition controller. The green limit status
light will go out; the heater will go through the normal post purge and
cool down cycle.
After the problem has been determined and corrected, push the
manual reset button on the backflow sensor, and follow the instruc
-
tions to relight the heater. Check for proper operation.
Maintenance
- A thin film of soot will form on the face of the backflow
sensor. At least once a month and during any routine heater cleaning,
open the viewport cover and clean the soot from the sensor. Check
the wire connections during scheduled maintenance inspections.
Troubleshooting Chart Guide
Symptoms
Follow
Troubleshooting Chart
With thermostat calling for heat, burner motor never attempts to
run (Green “power on” light is lit; Green “system ready” light is not lit). ...
Chart No. 1, page 39
Chart 1 check completed, but burner motor never attempts to run.
With thermostat calling for heat, burner motor runs momentarily. ............
Chart No. 2, page 41
System does not attempt to ignite. ...........................................................
Chart No. 3, page 42
Burner ignites and burns steadily until system goes into lockout. ............
Chart No. 4, page 43
Burner operation erratic/unstable flame pattern.
......................................
Chart No. 5, page 44
High temperature limit cycles.
..................................................................
Chart No, 6, page 45
Oil delivery system troubleshooting. .........................................................
Chart No. 7, page 47
CAUTION: The items on the Troubleshooting Charts that are marked with an
asterisk represent events that have occurred due to the improper function
-
ing of the heater. It is necessary to observe the operation of the heater to
determine what caused these events to occur.
B
ackflow
Sensor Switch
Continued