LAARS Mighty Therm2 MT2V (Sizes 500–2000 MBTU/h) - Install and Operating Manual - Manual (Page 32)

LAARS Heating Systems Page 32
SECTION 8.
Trouble Shooting
8.1 Resolving Lockouts
There are many causes of lockouts. The three most
common causes are: (1) inadequate gas supply, (2) poor
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. 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 flue 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-fired 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-fired 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 flow 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 inefficient and consequently, have very high gas
consumption. Because efficiency 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 efficiency. 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 briefly sniffing
the flue gases it is possible to determine if the CO
2
or O
2
is within the proper range. No significant flue 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 fire. To check the CO
2
, first 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 firing, 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 final 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 page.