Laars MASCOT LX, Руководство по обслуживанию

Страница: 65 / 94

59
Mascot LX Service Manual
DHW Flow Sensor (Hall Sensor) - Combi Units (MLXC)
Fig. B22-1 - DHW Flow Sensor
Flat-plate
water heater
DHW high
temperature
sensor
The DHW flow sensor senses demand from the Domes-
tic Hot Water piping. This unit includes a small paddle
that turns as the water flows past. As the paddle turns, a
magnet moves past a sensor and creates a signal for the
controller in the Mascot LX. (This sensor uses a prin-
ciple called the “Hall effect,” so this is sometimes called
the “Hall sensor.”)
The output from this sensor is a series of pulses at very
low voltage, so it is difficult to troubleshoot this type of
unit using a Volt-Ohmmeter. This sensor tells the control-
ler when there is a demand for domestic hot water. To
test the sensor, open a hot water faucet in the domestic
water system. The boiler should respond quickly. If it
does not, the sensor may be bad.
Tools and equipment required:
• Adjustable wrench or combination wrench set
• Pipe dope or Teflon® tape
Replacement procedure:
1. Turn off power to the system. Use the main disconnect switch mounted
on the front panel.
2. Isolate the boiler. Turn off the water shutoff valves located upstream and
downstream of the unit.
3. Drain the DHW piping.
4. The DHW flow sensor is mounted in the lower rear of the unit. See Fig.
B22-1.
5. Unplug the wiring connector (two wires). The connector is locked in
place by a “squeeze tab.” Press on the tab to release the connector.
6. Unscrew the sensor using a wrench. Turn counter-clockwise to unscrew
the part.
7. To reassemble, reverse the process we have just described. Be sure to
use pipe dope or Teflon® tape on the threaded part of the sensor.
B22