SER
VICE PR
OCEDURE
S
SER
VICE PR
OCEDURE
S
On-Demand Water Heater Service Handbook for 240, 340 & 540 Condensing Models • 33
the pressure-relief valve, the
system has a reversed connection.
Checking the Inlet
Gas Pressure and
Pressure Drop
This test is most effective when all gas
appliances on the supply line are operating.
1. Close the manual shut off valve at
the gas supply line inlet.
2. Open a hot water fixture. The unit
should turn on and the remaining
gas in the pipe line should purge
out. Close the water fixture
when the flame in the heater
extinguishes.
3. Turn power to the heater off by
unplugging it or closing the
external shutoff switch.
4. Remove the screw
from the pressure port
located on the gas inlet.
5. Connect a manometer
to the pressure port and
zero the manometer.
6. Slowly re-open the
manual gas valve.
Confirm that there are
no gas leaks.
7. Turn power to the water
heater on.
8. Open some of the hot
water fixtures that use
the highest flow rate
to turn on the unit.
Once the heater has
reached a steady firing
rate,
press and hold the
“MAX” button
on the
computer board
. (See
Checking for
a Crossed
Connection
1. Turn off cold water supply valve
to the water heater. If there are
pumps installed in the system for
recirculation, ensure that they are
turned off.
2. Turn on hot water at
one
fixture
in the structure. Make sure that
it is located at the highest point
possible. If possible, use the hot
side of a two-handle fixture. If you
must use a single-handle fixture,
make sure that it is open to the hot
side only.
•
After a brief time, the water
should drain completely.
•
If water continues to run, the
fixtures and plumbing system
need to be checked.
•
Cold water cross-connections
may be related to a recirculation
pump application, a defective
mixing valve, a bad check valve,
a missing check valve in the
application, or a cartridge in a
single-handle faucet that needs
to be replaced.
Checking for
a Reversed
Connection
1. Close cold water supply at the inlet.
2. Open the pressure-relief valve.
It should be installed on the hot
outlet side of the unit.
3. If water continues to run through
9. Record your gas supply pressure
(dynamic).
10. Release the “MAX” button and
close all of the water fixtures.
11. Record your gas supply pressure (static).
Gas Supply
Pressure Port
Figure
19
.
.
.
240 (T-H3J) / 340 (T-H3S) model
MAX bu
tt
on
MIN bu
tt
on
Increase bu
tt
on
Decrease bu
tt
on
540 (T-H3) model
MIN bu
tt
on
MAX bu
tt
on
Increase bu
tt
on
Decrease bu
tt
on
Manifold port
Computer board
To manometer
Tube
240 (T-H3J) / 340 (T-H3S) model
MAX bu
tt
on
MIN bu
tt
on
Increase bu
tt
on
Decrease bu
tt
on
540 (T-H3) model
MIN bu
tt
on
MAX bu
tt
on
Increase bu
tt
on
Decrease bu
tt
on
Manifold port
Computer board
To manometer
Tube
Figure 20.
Figure 21
