LAARS EDN Series - Installation, Operation and Maintenance Instructions - Manual (Page 34)

Page 34 LAARS Heating Systems Company
it is flashing three times, for ignition control lockout. If
it is, then that is a combustion lockout.
a. 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)” in Section 10.
If contamination of the air source is suspected,
check the vent system for leaks back into the
combustion air.
b. 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 A
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
and start the boiler. If lockout persists, check
the flame signal. The minimum flame current
necessary to keep the system from lockout is 1
microamp (A). There is no need to disconnect
anything to measure the flame current signal.
To measure the flame signal, connect an analog
DC microammeter to the FC terminals on the
ignition control, per Figure 37. The meter should
read 1A or higher. (If the meter reads below
“0” on the scale, the meter leads are reversed.
Disconnect and reconnect the meter for correct
polarity.) If the meter reading is less than 1A,
see the “poor combustion” section. (Check for air
leaks at inlet to blower.)
c. 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 boiler control should
light. If it does not, reset the boiler and check
for 24 VAC at the boiler control. If the voltage
is less than 20 VAC, and transformer voltage is
24 VAC replace the boiler control. 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.
d. 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 () ohms. If the resistance is not 50-100
ohms (), 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 boiler control or faulty
ignitor wires.
e. Blocked or contaminated air source: Before
proceeding, ensure that the vent terminal (Direct
Vent installations) or the air inlet (Category IV
installations) is not obstructed. In general, only
direct vent installations have the potential for
cross contamination (flue products entering the
combustion air stream) of the combustion air
source. This may be caused by leaky joints in the
3" flue pipe located inside the 5" combustion air
pipe. If this is suspected, remove the front panel
from the appliance, reset the boiler and allow it
Figure 37. Flame Sensor Current Check.