Laars MASCOT LX, Service Manual

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Mascot LX Service Manual
Flue Temperature and Flue Safety Sensors (continued)
The flue temperature and flue safety sensors will shut
down the Mascot LX unit if the stack temperature rises
above 195°F. This assembly is actually a “duplex” sen-
sor - it includes two separate thermistors. The control
system constantly compares the readings from the
thermistors. If there is a large difference between the
readings, or if one of the thermistors is “open” or “short -
ed,” the control system will shut down the Mascot LX
unit, and display an “E015” error message.
Replacement Procedure:
1. Turn off power to the unit. Use the main disconnect
switch on the front panel.
2. Turn off all gas valves supplying gas to the unit.
3. The stack temperature limit switch is mounted in the
exhaust duct on the right side of the boiler. See Fig.
B8-1. To get access to the switch, remove the upper
front panel of the cabinet.
4. The sensor assembly is held in place by a “press fit”
into a rubber grommet. Pull the sensor assembly
straight out.
5. Unplug the wiring connector (four wires). The con-
nector is locked in place by a “squeeze tab.” Press
on the tab to release the connector.
6. To test the part for accuracy, see Section B9.
7. To reassemble, reverse the process we have just
described.
Fig. B8-1 - Flue Temperature and Flue Safety Sensors
B8
cont.
Flue temperature
and flue safety
sensors