Hydronic Heating Boilers and Domestic Water Heaters Installation and Service Manual

29. Burners are now firing for approximately 50% of the
heater’s input.
30. 24VAC is supplied from the second stage of the electronic
temperature control across the 2C and 2NO terminals on
the terminal strip on to a control to a relay.
31. The control relay switches the fan on the 985,000 -
2,065,000 Btu/hr models to high speed and energizes the
gas valves for the remaining 50% of burner input.
32. The remaining gas valves open and supply gas to the
orifice inlet to pre-mix.
33. The gas/air mixture is forced out of the burner ports and
light by carryover from the burners currently firing.
34. The heater is now firing at full rated input.
HEAT TRANSFER PROCESS
35. Heated products of combustion pass over the heat
exchanger transferring heat to the water.
36. The rate of flue product movement is controlled by “V”
baffles on the heat exchanger to maximize heat transfer.
37. Flue products pass into the flue collector and are
exhausted from the unit.
END OF SEQUENCE
38. Set point for the high fire on the electronic temperature
control is satisfied.
39. Power to all valves is turned OFF on F9 systems and
power to the high fire gas valves is turned OFF on M9
systems.
40. The water temperature continues to rise and the set point
for low fire is satisfied (M9).
41. Power to the low fire gas valves is turned OFF (M9).
42. The combustion air fan runs for a 30 second post purge
timing and turns OFF.
43. The appliance is now in a Standby Mode waiting for the
next “call for heat”.
GLOSSARY
Power Supply
(AC120VAC/60Hz)
120VAC/60Hz/1PH power connects to black (line) and white
(neutral) wires located within an electrical wiring box located
on the left side of the unit. A green chassis grounding wire is
also provided for connection to earth ground.
ON/OFF Rocker Switch
The black line voltage wire runs directly to a single pole, single
throw On/Off rocker switch located behind the front cover
accessible by a thumb screw. Turning ON the rocker switch
delivers line voltage to the low voltage transformer and
ignition module.
Note: The On/Off switch does not provide for disconnection of
power being supplied to any remotely connected devices that
may be connected to the unit (i.e. pumps, louvers, power
venters, etc.,). As such, it may be necessary to locate and turn
off power to these items before attempting to service the unit.
Low Voltage Supply Transformer
A 120VAC to 24VAC transformer located within the control
panel provides 24VAC/60Hz to many of the components
located on the unit. One of its 24VAC outputs (blue) is
connected to a circuit breaker and the other (yellow) is
connected to chassis ground.
24VAC Circuit Breaker
A circuit breaker is provided on the 985,000 - 2,065,000 Btu/hr
models for protection of the low voltage supply transformer
from overloads and short circuits. The breaker is located inside
the unit on the lower right corner of the control panel. Power
from this breaker goes to the electronic temperature controller,
ignition module and various other components and/or options
on the unit. When tripped, all factory-installed 24VAC
components will lose their 24VAC power.
Manual Reset High-Limit Thermostat
A manual reset high limit thermostat is provided as backup for
the temperature controller. This will either be an adjustable dial
or fixed temperature bulb-capillary style thermostat that will
trip and require resetting should water temperature exceed its
settings. When tripped, all controls remain powered, but
24VAC is prevented from being delivered to the ignition
module's thermostat input.
EMS/Sequencer/Remote Aquastat
Terminals
The EMS/sequencer/remote aquastat terminals are provided
for connection of the unit to an external energy management
system or sequencer and are located along the top edge of the
terminal strip located within the electrical wiring box. In
addition to providing a means to externally stage fire the unit,
these terminals also provide for remote shutdown and override
by routing through dry contacts from external devices.
Connection of the external dry contacts to these terminals
requires the removal of one or more factory installed jumpers
located on the terminal strip.
Safety Device Terminals
The safety device terminals ensure that no power can be
delivered to the ignition module unless factory/field-installed
safety devices such as flow switches and gas pressure switches
are closed. These safety device terminals are located below the
EMS/Sequencer/Remote Aquastat terminals located within the
electrical wiring box. Two types of connections are offered:
Continuous terminals provide for connection of safety devices
that are desired to be constantly monitored. Intermittent
terminals are provided for devices that are only monitored
during a "call for heat" cycle. Connection to either of these
terminals requires the removal of a factory-installed jumper
located on the terminal strip.
Installation and
Service Manual
45