Mighty Therm
2
(200, 300, 400)
Page 33
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 40 seconds, and then the unit will light.
If it does not, check the gas supply pressure to
the appliance, after resetting the appliance and
attempting another start-up. The gas pressure to
the appliance must be above 5 in. w.c. (1.2 kPa)
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. 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
Boiler short cycling is caused when the load
on the boiler system swings rapidly causing frequent
cycling between call for heat and satisfied conditions.
This condition is greatly reduced on two stage
units. If short cycling is a problem, it may be due
to an oversized boiler, incorrect set points or a load
distribution problem. If desired temperature response
is not achievable without short cycling it may be
necessary to install a buffer tank in the system. 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. 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. The CO
2
should be 8% at high fire for
natural gas and 9.2% at high fire for LP. To check the
CO
2
, first verify that the supply gas pressure is within
5 to 13 in. w.c. (1.2 to 3.2 kPa). With the Mighty
Therm2 running with all stages firing, set the air box
pressure to 1.8 in. w.c. (0.42 kPa) (as a starting point),
by adjusting the air shutter(s) at the intake of the
fan(s). Check the CO
2
, and adjust the air shutters if
further adjustment to the CO
2
is needed.
