27
System Troubleshooting
Start system by setting thermostat or controller above room
temperature and observe system response.
Establish type of system malfunction or deviation from
normal operation by using Pilot System Troubleshooting
Table, in following section.
Use table by following questions in boxes. If condition is
true (answer is yes), go down to next box. If condition is
not true (answer is no), go to box alongside.
Continue checking and answering conditions in each box
until problem and/or repair is explained. Use Component
Checks section, see below, as necessary, to perform system
checks.
After any maintenance or repair, troubleshooting sequence
should be repeated until procedure ends with normal
system operation.
COMPONENT CHECKS
Check Spark Ignition Circuit
Electronic module and step-up transformer in control provides
spark ignition at 15,000 V (open circuit). Check circuit at
control module as follows:
1.
Turn off manual gas valve to prevent fl ow of gas.
WARNING
Electrical shock hazard. Do not touch either end
of jumper or stud terminal, high voltage circuit.
Failure to follow these instructions could result in
death or serious injury.
!
2.
Disconnect ignition cable at control stud terminal to
isolate circuit from pilot burner/igniter-sensor, and
prepare short jumper lead using heavily insulated wire,
such as ignition wire.
3.
Energize control and touch one end of jumper fi rmly to
control ground terminal (GND). (Do not disconnect
existing ground lead.) Move free end slowly toward
stud terminal to establish spark. Pull lead wire slowly
away from stud. Note length of gap at which arcing
discontinues.
4.
Arc length of 1/8 inch (3.2 mm) or more indicates
satisfactory voltage output. If no arc can be established
or maximum gap is less than 1/8 inch (3.2 mm), replace
control.
Control Functions And Operation
The control module performs the following basic functions:
1.
Opens and closes the fi rst (pilot) operator of the gas
valve.
2.
Provides a spark for igniting pilot burner.
3.
Senses the pilot burner fl ame.
4.
Shuts off the spark after pilot fl ame is lit.
5.
Opens and closes the second (main) operator.
These functions occur in two stages - trial for pilot ignition
and main burner operation as described below.
Trial For Pilot Ignition
On every call for heat (system start), control performs
internal safe-start check. If fl ame simulating condition is
present, system will not start.
During normal start, control opens fi rst (pilot) valve
operator of gas control, which allows gas to fl ow to pilot
burner. At same time, electronic spark generator in control
produces 15,000 Volt spark pulse output (open circuit).
This voltage produces spark at igniter sensor rod which
ignites pilot burner. If pilot fl ame does not light or presence
of pilot fl ame is not detected back through fl ame-rod,
control will not open second (Main) valve operator of gas
control. Control will continue to try to ignite pilot burner
until either fl ame is detected or thermostat (controller) is
set down below call for heat.
Main Burner Operation
When pilot fl ame is established, fl ame rectifi cation circuit is
completed to burner ground. Control fl ame sensing circuit
detects fl ame current, shuts off spark generator and opens
second (Main) valve operator to allow gas to fl ow to main
burners. Pilot fl ame ignites main burner conventionally.
IMPORTANT: Electronic control module cannot be repaired.
If troubleshooting procedure indicates malfunction in control,
control must be replaced. Intermittent Pilot systems should be
serviced only by trained, experienced service technicians.
Preliminary Check
Following visual checks should be made before
troubleshooting and after maintenance.
1.
Check power switch.
2.
Manual shutoff valves in gas line to boiler must be
open.
3.
Make sure all wiring connections are clean and tight.
4.
Review control’s normal sequence of operation.
OPERATION AND SERVICE
