8
PHTM II
Combi Installation, Operating & Service Instructions
110331-07 - 8/23
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, 3-way 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
signal 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 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 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 set point
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
Internal boiler pump provides flow through heat
exchanger.
17.
Automatic air vent
Connected to pump outlet, air vent helps remove
air from water system.
18.
Boiler flow switch (UL 353 Listed)
Proves water is present in boiler and flow rate is
adequate prior to starting boiler.
19.
DHW flow sensor
DHW flow sensor monitors DHW water demand.
When DHW detects DHW draw greater than 0.5
gpm, boiler control initiates a DHW heat demand.
20.
Plate heat exchanger
Heats domestic water using boiler water.
21.
3-way valve
When DHW flow sensor detects flow and DHW
has priority, 3-way valve is positioned to direct all
boiler water to plate heat exchanger. When CH
demand has priority, valve is positioned to direct
all boiler water to CH zones. 3-way valve's default
position is DHW.
22.
DHW temperature sensor
Used to monitor DHW water leaving plate heat
exchanger. Boiler control uses DHW water
temperature to initiate DHW burner demand and
adjusts boiler firing rate to maintain DHW setpoint
temperature.
23.
Flow Limiter
Provides flow restriction to 6 gpm (23 L/min). See
Table 3-1 for DHW draw rates.
24.
Condensate trap (not shown)
Allows combustion chamber and vent condensate
to drain from boiler while retaining flue products in
boiler.
25.
Combi Black Drain (not shown)
used to drain
hydronic side water.
