A.O. Smith TWI 35-200, Installation, User And Service Manual

Page: 50 / 92

8.9.2 Air pressure differential
Check the air pressure differential across the air pressure switch:
1.
Disconnect hose H of the air proving switch and connect this side of the hose to the
+ of the pressure gauge.
2. Disconnect hose L of the air pressure switch and connect this side of the hose to the
- of the pressure gauge.
3. Turn on the water heater (see 4.1).
4. Read the pressure value from the pressure gauge while the water heater is pre-
purging.
5. Compare the measured value to the value from the table (see 13.1).
Note
When the air pressure differential is not correct, refer to Displayed errors (see 12.1.2),
error LDS with code XAC–XXXX.
6. Set the control switch on the front of the water heater to 0 to turn off the water
heater.
7. Disconnect the pressure gauge.
8. Reconnect the hoses of the air proving switch and the gas valve.
Fig. Air pressure differential
H
L
8.9.3 Gas supply pressure
Check the gas supply pressure:
1.
Loosen the sealing screw (2) of the test nipple by a few turns.
Note
Do not completely loosen the sealing screw, it can be difficult to retighten it.
2. Open the gas supply to vent the gas pipes through the test nipple.
3. Connect a pressure gauge to the test nipple as soon as you smell gas.
4. Turn on the water heater (see 4.1).
5. If necessary, create a heat demand:
-
Use a hot water draw-off point to tap water, or
- Raise the setpoint of the water temperature, refer to Set the water
temperature.
6. Wait about 1 minute.
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50 Installation, Maintenance and Service part