Service Procedure I: Thermostat Circuit Testing And Replacement - Bradford White UCG100H399 Service Manual

High Limit (Overheat
80
DHW/TEMP
93
Sensor Fault
Flame detected out of
105
Ignition Failure
110
Light-off Rate Proving
122
137
(Interlock Open)
16
Service Procedure I:
Condition)
sequence
Occurred
Failed
ILK Open
Check the wiring from the sensor to the control module.
Measure the resistance of each outside wire to the center wire.
If either outside wire has a much different resistance reading, replace
the sensor.
Make sure the sensor is securely held inside the well with the clip.
If the problem persists and the sensor and wiring check O.K., then
replace the control module.
Check the sensor wire harness from the sensor to the control module.
Make sure there are no loose connections to the control plug.
Check the resistance reading from each of the outside wires to the
center (common) wire.
If the ohm readings are not fairly close, replace the sensor.
Replace the control module if the problem persists and the sensor and
wire connections are not defective.
Check to see if flame is present inside the combustion chamber before
or after the ignition cycle.
If so, check to make sure the gas valve is wired correctly.
Check for voltage at the gas valve connection.
Replace the gas valve if defective.
If no flame is visible outside of the ignition sequence/run cycle, then
make sure the flame sensor is wired to the correct terminal.
Make sure the ignition cable is not crossing the flame sensor wire or
ignition ground wires.
If problem persists and all other checks have been verified, replace the
control module.
Burner failed to light or stay lit after 3 retries.
Hold condition – will reattempt ignition after 15 minute waiting period.
Check gas valve wiring and gas valve operation during the ignition
cycle.
If burner lights but quickly goes out, check the flame sensor wire or the
flame sensor.
If the flame sensor rod is badly corroded with deposits, clean with
sandpaper or replace.
Check the inlet gas supply to make sure the pressure is sufficient and
does not drop after the gas valve opens.
Make sure the combustion blower is operating during the ignition and
run cycle.
Check the venting system to make sure the inlet and exhaust terminals
and venting system is not blocked.
If blower speed is not verified from the PWM (Pulse Width Modulation)
signal within 5 minutes, the previously described error code "62"
changes from a hold condition to this lockout code condition.
Check the harness and pin terminals for a good connection to the
control module.
Replace the control module if the wire harness is good.
Check if blocked vent safety switch is open.
If switch checks O.K., replace control module
16