Paloma PH2-20R OFN, Engineering Handbook

Page: 5 / 172

SVC 820-Tankless Gas Trouble Shooting Manual Page | 5
5
Sequence of Operations
ACTION EXPLANATION
Hot water faucet is open creating a demand Hot water draw initiates water flow thru the water
heater
Water flows thru the Water Flow Sensor Minimum flow rate of .4 GPM to activate @ 35
o
T
Control Board senses the flow rate has reached a
minimum demand of .4 GPM@ 35
o
T
Control Board is the ‘brains’ of the machine and controls
all input and actions during sequence of operations
Blower Motor conducts a pre-purge Pre purge is designed to verify we have a clear and clean
vent and supply oxygen to burner for proper ignition
The Proportional Gas Flow Regulator allows the
gas to flow to the main burner Proportional Gas Flow Regulator initially opens to 75% of
BTU input
Simultaneously, the Igniter Rod sparks and ignites
the main burner The Igniter Rod ignites the fuel in the main burner area.
All burners will fire initially
After ignition, the Flame Rods sense and monitor
the flame and ensure proper combustion The purpose of the flame rods is to verify flame and
proper combustion. In the event of flame failure or
improper combustion, the unit will go into an error code
The “In Use Indicator” on the remote control turns
“ON” (Red) and the “Priority Indicator” is Green
(multiple remote controls) Main burner is now lit. The PCB goes thru a series of
calculations (input sensing) to balance out the cold-water
temperature, the thermostat setting, the hot outlet
temperature, and the BTU required to heat the water.
The Proportional Gas Flow Regulator continuously
adjusts the gas volume in order to maintain the
outlet temperature. The water flow sensor also
adjusts the proper amount of cold water mix flow
to supply a stable hot water temperature at all
times. A signal is also sent to the Blower Motor in
order to constantly maintain the correct
proportion between gas and air volumes The PCB is constantly monitoring all of these inputs and
actions to ensure the outlet water temperature is within
1-5 degrees of thermostat setting. It also monitors the
BTU required to heat the cold water to the thermostat
setting and adjusts the gas valve accordingly
(Indoor Models Only) When the air intake is
blocked, or oxygen is not sufficient, the output of
the Flame Sensor changes The PCB senses this change and controls the Fan and Gas
Valve in order to prevent imperfect combustion. If the
PCB cannot correct such condition, the unit will go into
an error code
When the hot water tap is closed, the flow rate
signal from the water flow sensor stops Gas valve is closed. Main burner shuts off
The Fan continues to run for a few minutes Purpose is to cool the heat exchanger, exhaust all
combustions gases, and to maintain the burner chamber
charged with air for immediate ignition if there is
another hot water demand