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NORMAL OPERATION
Becoming familiar with how a tankless
water heater normally operates may
help to troubleshoot it. Assuming it
is properly installed with appropriate
gas, water, and electrical connections,
it should operate as follows:
Ac va on
1. A hot water fixture is opened. The
flow sensor must detect a flow rate
through the heater that is greater
than the 0.4 GPM before the
heater will begin operation. The
temperature rise must be great
enough to meet the minimum input
requirement which is 9,000 Btu/h
for NG and LP. Otherwise, the
heater will remain in standby.
2. The fan activates to purge the system.
3. The Igniter generates a spark to
ignite the gas.
4. The gas valve will open. You will
hear a deep "clunk clunk" noise.
5. Once a flame is detected, the
green "In Use" LED will activate.
(This green LED is located on the
temperature controller or remote
controller.)
Opera on
6. The fan will modulate and the
gas solenoid valve assembly will
adjust based on the amount of
energy input required to meet the
demand.
7. If the water flow exceeds the water
heater's capabilities to heat to the
desired temperature, the flow control
valve will restrict the flow to ensure
6
•
On-Demand Water Heater Service Handbook for X3P Models
delivery of water at the desired
temperature. This will result in a
loss of pressure at hot water fixtures
whenever flow is restricted through
the water heater.
NOTICE: The bypass component acts
like a mixing valve. It helps to maintain
the desired outlet temperature and
reduce damage to the heat exchangers
due to corrosion and erosion. The
bypass valve is also used when
multiple water heaters are linked
together.
Shutdown
8. The heater will stop heating when
the water flow rate drops below
the deactivation point of 0.26 GPM.
9. The heater will close the main
gas valve and solenoid gas valves,
extinguishing the flame.
Gas solenoid valve
Fan motor
Gas valve
Flame rod
Hi-limit
Thermistor
Thermistor
Bypass valve
Water control valve
/Flow sensor
Heater
Thermistor
Thermistor
Hot water
Return line
Figure 1: The purpose of this diagram is to illustrate tankless water heater design concepts, and may
not be accurate to the unit's physical description.
10. When the flame sensor no longer
detects a flame, the green "In Use"
LED will turn off.
11. The fan will increase in speed to
purge any remaining exhaust gases.
The length of post-purge can last up
to 1-½ minutes.
12. The heater will enter standby
mode.
Preliminary
Checklist
To get started, review the following
topics. You may also refer to "General
Issues," if necessary.
Gas/Water/Electric:
•
Verify that the correct gas type
is being used. Check the supply
gas, the gas type DIP switch,
and the gas type shown on the
Intake
Exhaust
Exhaust thermistor
Pressure sensor
Venturi
Air adjustment valve
Stepping motor
Metal knit burner
Igniter
Igniter rod
Primary heat exchanger
Secondary heat exchanger
Exhaust duct
PCB
Thermo switch
Condensate drain port
Gas
TM
X3
Filter
Cold water
.H.
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