Water Flow - A.O. Smith TC-049R3 Service Handbook

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
Residential Gas - continued
When a hot water faucet is opened, water pressure from the well tank or street

Water Flow:

main forces cold water into the water heater. This pushes hot water out of the tank.
A residential water heater is not a precise operating appliance. Because the water
Operation:
heater relies on the expansion and contraction of a metal rod, when the thermostat dial is set at
an indicated setting ("σ" is recommended as a starting setting. This is approximately 120 degrees
F.) the heater may shut off at 110 to 130° F. The heater will consistently shut off at this same
temperature. For this same reason, water temperature may drop 15 - 25° F, around the
temperature probe, before the main burner is activated. Keep in mind that hot water in the upper
part of the tank will probably be very near the "shut off" temperature of the control while incoming
cold water drops the water temperature around the thermostat probe. Also, short repeating
heating cycles caused by small hot water uses can cause temperatures at the point of use to
exceed the thermostat setting by up to 30° F.
Setting Approximate Temperature (°F) Time To Cause Injury
Hot (▲)
A
B
C
Very Hot
A.O. Smith Water Products Company
©2005
SERVICE HANDBOOK
120° ± 10°
130° ± 10°
140° ± 10°
150° ± 10°
160° ± 10°
9
5 Minutes
30 Seconds
5 Seconds
1.5 Seconds
Under 1 Second
Technical Training Department
Ashland City, TN