LAARS Mighty Therm2 MT2P (Sizes 500–2000 MBTU/h) - Install and Operating Manual - Manual (Page 24)

LAARS Heating Systems Page 24
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, and 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 appliance,
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
). MT2P 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, and the
gas pressure is at least 5" w.c., ignitor failure may
be the cause. Check the ignitor by unplugging
it, allowing it to cool to room temperature, 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
Because of the large mass of pool systems, short
cycling should not exist. If it does, it will be caused by
insufficient flow in the pool loop. Check that there is no
blockage in the pool loop such as a plugged or partially
plugged pool filter.
8.4 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% natural gas (9.2% LP) 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 MT2P running with both
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.
Models 1250, 1500, 1750 and 2000 have two blowers and
two air chambers (boxes). The pressure of each air box
must be equal when the final adjustment is made.
8.5 Troubleshooting the Pool Heater
Temperature Control
With a Voltmeter, test for 24 VAC between terminals
1 & 2 on the 10 pin connector. Check that the sensor
temperature is lower than the setpoint temperature by
at least the differential setting. If this is true, check that
there is 24 VAC at the yellow wire on the 4 pin connector.
If there is not 24 VAC, check that the high limit is not
open. If there is 24 VAC at the yellow wire on the 4 pin
connector and not at the light blue wire on that connector,
replace the control.
8.6 Troubleshooting MT2P Controls
The MT2 series consists of two models with one
ignition module (500 & 750) and five models with two
ignition control modules (1000-2000).
A diagnostic/power distribution terminal strip is
located in the upper control panel. To access this remove
the high limit/ignition control panel cover. Trouble-
shooting can be accomplished by using a voltmeter to
verify 24-volts has energized individual components.
Ladder diagrams for models 500-750 are shown in
Figure 7 . These models have one ignition control and one
inducer. This inducer is powered directly from the Fenwal
ignition control's “Fan Connections”. The wire diagrams
for these models are located in Figure 10 .
The ladder diagram for model 1000 is shown in
Figure 8 . This model has two ignition controls and one
inducer. This inducer is powered directly from the Fenwal
ignition control's “Fan Connections”. The wire diagrams
for these models are located in Figure 11 .
Ladder diagrams for sizes 1250-2000 are shown in
Figure 9 . These models have two ignition controls and
two inducers. This inducer is powered indirectly from
the Fenwal ignition control's “Fan Connections” via two
120-volt switching relays. When either ignition module
receives a call for heat, it switches its blower to high
speed and the blower of the idle ignition module to low
speed. The wiring diagram is shown in Figure 12 .