Flame Sensor; Water Temperature Limit Controls - A.O. Smith XB1000 User Manual

FlAMe SeNSor

Each burner is equipped with a flame sensor to detect the
presence of the burner flames at high and low fire conditions. If
no flame is sensed, the gas valve will close automatically. The
voltage sensed by the flame sensor will also be displayed on the
Burner Screen.
FiGUre 6. FlAMe SeNSor

WATer TeMperATUre liMiT CoNTrolS

The "XB/XW" models incorporate an outlet water sensor having
dual sensors, that are factory set at 210°F (99°C).
MAiN poWer SUpplY SWiTCh
The main power supply switch is a padlockable switch. This switch
pro vides 120V from the power supply to the boiler.
This switch needs to be turned off when servicing the boiler.
NoTe: The enable/Disable Switch on the front of the boiler
does not interrupt electrical power to the boiler.
FiGUre 7. MAiN poWer SUpplY SWiTCh
WATer TeMperATUre SeNSorS
FiGUre 8. WATer TeMperATUre SeNSorS
Temperature sensors
Temperature probes have embedded temperature sensors
(thermistors). The boiler's control system monitors these sensors
to determine water temperature at various points in the system.
iNleT AND oUTleT TeMperATUre SeNSorS
All models have two inlet and two outlet temperature sensors
for each heat exchanger, factory installed to monitor the water
temperature entering and leaving the boiler. The Inlet Probe is
a temperature sensor only and has two leads. The Outlet Probe
also contains the manual reset high temperature limit switch
and has four leads. The control system displays the Inlet and
Outlet water temperatures sensed from these two sensors on the
default Temperatures screen.
reMoTe SeNSorS
All models are supplied from the factory with a remote sensor.
The remote sensor is used to control system water temperature
for a single boiler in a domestic hot water storage tank or in the
return line from a primary/secondary hydronic heating system.
The boiler will modulate its firing rate in response to the
actual system temperature and load conditions. The control
system displays the temperature sensed from the remote sensor
as the "Lead Lag" temperature on the default Temperatures screen.
loW WATer CUToFF DeViCe (lWCo)
Low water cutoff device is normally a closed switch that opens
when water drops below a preset level. Each model is equipped
with a factory installed LWCO. LWCO board is connected to the
electronic panel, whereas the sensor probe is connected to the
heat exchanger.
FiGUre 9. lWCo boArD AND probe
7
are threaded immersion probes.