LAARS NeoTherm NTV (Sizes 399-850 MBTU/h) - Service Manual - Manual (Page 60)

50
Service Manual - NeoTherm 500
Fig. B30-1 - Outlet water temperature sensor (typical)
The outlet water temperature switch allows the control
system to monitor the temperature of the water as it
leaves the NT unit. A typical installation for the outlet
water temperature sensor is shown in Fig. B30-1. The
sensor is connected to J8 8-9-10 on the control module.
This sensor assembly includes two electronic devices
called “thermistors.” As long as the resistance readings
from both sensors agree, the Magna-Therm will continue
to operate. 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 NT unit and
display a “Hold 92” error message.
For instructions on testing the assembly, see Section
B32.
To reset the control system after the outlet sensor trips:
• On a unit with the original (white) user interface -
Press the Reset button near the lower left-hand
corner of the display. This will reset the lockout, and
the lockout code will disappear.
• On a unit with current user interface -
Reset by pressing the OK button.
Removing and Replacing the Outlet Water Temperature Sensor
See Fig. B30-1 for a typical installation.
Tools and equipment required:
• Crescent wrench or 14 mm socket
• Pipe dope or Teflon® tape
Procedure:
1. Turn off power to the system. Use the main disconnect switch mounted above
the front panel.
2. Isolate the boiler. Turn off the water shutoff valves located upstream and down-
stream of the unit.
3. Drain the boiler. The drain valve is located near the lower end of the heat ex-
changer.
Sensor
Water outlet
pipe
B30
Outlet Water Temperature Sensor
B31