8
110332-04 - 2/23
PHTM II
Installation, Operating & Service Instructions
4
How It Works
1.
Heat exchanger
Water flows through heat exchanger's stainless
steel tubes. Heat is transferred to water as flue
products are cooled below point of condensation
for maximum heat transfer and efficiency. An
enclosure contains and directs flue products to
vent piping.
2.
Blower
Pulls air and gas through venturi. Air and gas
mixture is then pushed into burner where it burns
inside combustion chamber.
3.
Gas valve
Precisely controls gas flow rate in response to
electronic signal from control.
4.
Venturi
Creates suction at gas valve outlet and mixes air
and gas before they flow into blower.
5.
Burner (not shown)
Constructed of stainless steel, burner uses
pre-mixed air and gas to meet modulation
requirements.
6.
Boiler control (not shown)
Monitors internal and external sensors and
controls blower, gas valve, and pumps to meet
heating and DHW demand. Control is a "gas
adaptive system" that regulates air and gas
flow mixture by measuring flame ionization and
adjusting gas valve to achieve a target air-fuel
ratio. This eliminates need to make throttle screw
or offset adjustments. System is self-calibrating
and continuously maintains air-fuel ratio at desired
value.
7.
120 VAC connection board
Provides field connections for line voltage boiler
pump and two additional pumps (system pump
and aux. pump).
8.
Low voltage connection board
Provides field connections for thermostats,
external limits, remote firing devices (4-20mA
or 0-10V), header sensor, outdoor sensor and
LWCO.
9.
Control enclosure
Houses boiler control and provides access to
installed fuses and spare fuses.
10.
Local user display
Allows review of boiler status and parameter
adjustment. In event of fault condition, LCD
display turns red and fault condition is displayed.
11.
Flue temperature sensor
Used to monitor flue gas exiting boiler. Boiler
control will alarm, reduce boiler firing rate and
shut down boiler if flue gas temperature is too
high.
12.
Boiler supply temperature sensor (UL 353
Listed)
Dual element temperature sensor used to monitor
boiler water exiting heat exchanger. Boiler control
uses supply temperature to initiate CH burner
demand, adjust firing rate to maintain CH setpoint
temperature and shut down the boiler if supply
temperature is too high.
13.
Boiler return temperature sensor
Used to monitor boiler water entering heat
exchanger.
14.
Ignitor/flame sensor
A single ignitor/flame sensor is used to both
provide ignition energy and monitor flame.
15.
Air pressure switch
Proves air flow (closes) prior to boiler ignition.
Switch is proven open prior to starting blower.
16.
Boiler Pump, field installed (not shown)
External boiler pump provides flow through heat
exchanger.
17.
Boiler flow switch (UL 353 Listed)
Proves water is present in boiler and flow rate is
adequate prior to starting boiler.
18.
Condensate trap (not shown)
Allows combustion chamber and vent condensate
to drain from boiler while retaining flue products in
boiler.
