Laars MIGHTY THERM2 - Delayed Ignition - Possible Causes; Short Cycling - Boiler; Short Cycling - Water Heater; High Gas Consumption

LAARS Heating Systems
Page 32
combustion, (3) ignitor failure.
1. Inadequate gas supply: Before proceeding, ensure that
the gas supply has not been shutoff or the LP tank (LP
boilers) is not empty.
If your boiler is equipped with the optional gas
pressure switches, then the Low Pressure switch might
have tripped and will need to be reset.
Then, restart the boiler and observe the operational
cycle. After a 15-second fan pre-purge, the ignitor will
heat up for 20 seconds, and then the unit will light. If
it does not, check the gas supply pressure to the ap-
pliance, after resetting the appliance and attempting
another start-up. The gas pressure to the appliance must
be above 5" W.C. (1.2kPa) throughout the entire start-
up cycle. If it is not, correct the supply problem (check
gas valves or supply piping). If the supply pressure is
adequate, consult the factory for assistance.
2. Poor combustion: Poor combustion should be
suspected if there is a strong ue gas odor. The odor
may result from an improper gas/air ratio (high or low
O
2
or CO
2
). Mighty Therm2 appliances operate best
with 45% excess air (8% CO
2
on natural gas, 9.2% CO
2
on LP). Check the CO
2
of the appliance and adjust if
necessary.
3. 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 50-80 ohms at room temperature. If the
resistance is not 50-80 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 faulty ignitor wire harness or the
ignition control.
8.2 Delayed Ignition — Possible Causes
A defective burner can cause a delayed ignition. If
the gas supply pressure is proper and the gas valves are
functioning properly, then burners should be inspected.
There should be no distortion or perforations in the burners
outside of the active burner port area. Replace if indicated.
8.3 Short Cycling — Boiler
Because the Mighty Therm2 is a stage-red boiler,
and its input will decrease when there is a reduction
in heating load, short cycling is greatly reduced. If
the heating load drops below the minimum input of
the boiler for an extended period, the boiler will have
a tendency to short cycle. This can be a symptom
of improper control strategy or setpoints, or a load
distribution problem. Contact your Laars representative
to discuss possible remedies.
8.4 Short Cycling — Water Heater
Short cycling will generally occur only in combination
space heating and water heating applications when the water
heater is operating in the space-heating mode. Because the
Mighty Therm2 is a stage-red water heater and its input
will reduce when there is a reduction in heating load, short
cycling is greatly reduced. If the heating load drops below
the minimum input of the water heater for an extended
period, the water heater will have a tendency to short cycle.
If short cycling is frequently experienced, regardless of
the control’s attempt to limit it, the heating load should be
redistributed to control it.
If short cycling occurs in a water heater application, it
is probably caused by undersized piping between the water
heater and the storage tank or by some other factor that
restricts proper water ow through the water heater. The
cause should be determined and corrected.
8.5 High Gas Consumption
Appliances operating with an improper air/fuel ratio
are very inefcient and consequently, have very high gas
consumption. Because efciency is high when the CO
2
is high (or O
2
is low), appliances operating with low CO
2
or high O
2
(especially LP appliances) consume more
gas. Adjust the CO
2
or O
2
for optimum efciency. If no
combustion analyzing equipment (CO
2
or O
2
) is available
then a proper adjustment of the air/fuel ratio (CO
2
or O
2
)
cannot be accomplished. However, by briey snifng the
ue gases it is possible to determine if the CO
2
or O
2
is
within the proper range. No signicant ue gas odor should
be detected when combustion is proper. A strong piercing
smell indicates poor combustion and generally a lean
mixture - low CO
2
or high O
2
. The CO
2
should be 8% at
high re. To check the CO
2
, rst verify that the supply gas
pressure is within 5" to 13" w.c. (1.2 to 3.2 kPa) With the
Mighty Therm2 running with all stages ring, set the air
box pressure to 1.5" w.c. (0.37 kPa) (as a starting point), by
adjusting the air shutter(s) at the bottom of the fan(s). Check
the CO
2
, and adjust the air shutters if further adjustment to
the CO
2
is needed. Sizes 1250 to 2000 have two blowers and
two air chambers (boxes). The pressure of each air box must
be equal when the nal adjustment is made.
SECTION 9.
Replacement Parts
Only genuine Laars replacement parts should be used.
9.1 General Information
To order or purchase parts for the Laars Mighty
Therm2, contact your nearest Laars dealer or distributor.
If they cannot supply you with what you need, contact
Customer Service (see back cover for address, telephone
and fax numbers).
9.2 Parts List - see next pages.