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RESIDENTIAL GAS, NON POWER VENTED, WATER HEATER
SERVICE HANDBOOK
State Water Heater Technical Training Department
© 2004 Ashland city, TN
9
Residential Gas - continued
Water Flow: When a hot water faucet is opened, water pressure from the well tank or street
main forces cold water into the water heater. This pushes hot water out of the tank.
Operation: A residential water heater is not a precise operating appliance. Because the water
heater relies on the expansion and contraction of a metal rod, when the thermostat dial is set at
an indicated setting (“▲” 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 Produce 2
nd
& 3
rd
Degree Burns on Adult Skin
Hot (▲)
120° ± 10° 5 Minutes
A 130° ± 10° 30 Seconds
B 140° ± 10° 5 Seconds
C 150° ± 10° 1.5 Seconds
Very Hot 160° ± 10° Under 1 Second