LAARS EDN Series - Installation, Operation and Maintenance Instructions - Manual (Page 31)

Endurance Page 31
temperature rises rapidly and the safety
limit operates, the internal pump is not
operating. Refer to the wiring diagrams and
check for voltage (120V)
across the terminals on the PCB marked PMP.
a.
If there is no voltage, and the PCB
display does not indicate on or off,
replace PCB
b. If there is voltage, the pump or wiring
is defective.
F-3 Attempt to start the boiler. Check
combustion air blower operation. If F-3 is
indicated again, replace blower.
F-4 Check for damaged wiring or poor
connection at sensor plug. If they are OK
disconnect the sensor plug and check the
resistance across the sensor terminals. The
resistance of a good sensor is 10,000 ohms
@ 77°F (25°C). Replace sensor if
resistance is less than 500 or more than
20,000 ohms.
F-5 Correct in the same manner as F-4.
F-6 Correct in the same manner as F-4.
8.2.3 Resolving Lockouts (LO)
The memory does not need to be accessed.
Memory fault codes are for error history only. All
thermistor faults will show as “F” codes on the
LED, and will never cause the LED to read “LO”.
There are many causes for lockouts. The five
most common causes are: (1) poor combustion,
(2) poor flame sensor signal, (3) inadequate gas
supply, (4) ignitor failure, (5) blocked or contaminated
air source.
1. Poor Combustion: Poor combustion should be
suspected if there is a strong flue gas odor. The
odor may result from either an improper gas/air
ration (high or low CO
2
) or contamination of the
combustion air supply. If an improper gas/air
ratio is suspected refer to “gas valve calibration
(offset adjustment)” on page 25. If contamination
of the air source is suspected refer to (5) below.
2. Poor flame sensor signal: The boiler control
board will lockout if the flame sensor is
grounded or if the flame signal it receives is less
than 1
mA dc. To check for a grounded sensor,
remove the flame sensor wire (yellow) from the
boiler control board and check for continuity
between the yellow wire terminal and the
combustion chamber bottom pan. If there is
continuity, the flame sensor is grounded. An
alternate way to check for grounding of the
flame sensor is to check the ohms resistance
between the yellow wire terminal and the
combustion chamber bottom pan, using a meter
set for at least 100,000 ohms. The resistance
must be more than 250,000 ohms (some
technicians have been confused by meters which
report infinite resistance with what appears to
them as double zeros; an infinite resistance
reading means there is no grounding of the flame
sensor.) If there is continuity, or the ohms
resistance is less than 250,000 ohms, debris or
moisture in the combustion chamber may be the
cause. To correct, carefully remove the ignitor
and flame sensor assembly. Look for debris on
the assembly where the flame rod exits the
ceramic tube. If debris exists, remove it. If this
area is clean, insert a pencil or other round object
into the flame sensor hole in the bottom
combustion chamber pan and roll it around to
clear any debris that may exist inside the
combustion chamber. Replace the ignitor/flame
sensor assembly, reconnect the yellow wire on
the PCB and start the boiler. If lockout persists,
check the flame signal. To check the flame
signal, disconnect the yellow wire from the flame
sensor, connect a meter, set for microamps (
mA)
DC, between the flame sensor connector and the
yellow wire connector. Start the boiler. If the
meter reading is less than 1.00
mA DC, see (3)
“poor combustion” below. (Check for air leaks at
air inlet to blower.)
3. Inadequate gas supply: Before proceeding,
ensure that the gas supply has not been shutoff or
the LP tank (LP boilers) is not empty. Then, reset
the boiler and observe the operational cycle.
Approximately 20 seconds after the start of the
cycle, the GV LED on the PCB should light. If it
does not, reset the boiler and check for 24 VAC
at the plug on the PCB. If the voltage is less than
20 VAC, and transformer voltage is 24 VAC
replace the PCB. If the voltage is correct,
connect a pressure gauge to the offset pressure
port on the gas valve. Reset the boiler and
observe the offset pressure at startup and after 20
seconds. The pressure will be ~ -2 in. w.c. at
startup (during prepurge) and should become less
negative (-0.1 in. w.c.) when the gas valve opens
and gas flow starts. If the pressure remains at ~ -
2 in. w.c. throughout the cycle replace the gas
valve.
4. Ignitor failure: If the boiler goes through a
normal start cycle but combustion does not
occur, ignitor failure should be suspected.
Check the ignitor by unplugging the ignitor plug
and measuring the ignitor resistance. It should be
50-100 (
W) ohms. If the resistance is not 50-100
ohms (
W), replace the ignitor. If the resistance is
correct, reset the boiler and check for 120 VAC
at the ignitor plug during the start cycle. If there
is no voltage, replace the PCB or faulty ignitor
wires.
5. Blocked or contaminated air source: Before
proceeding, ensure that the vent terminal (Direct