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Thermostat Operation: Standard residential water heaters use mechanical thermostats. With a mechanical
thermostat, a dial setting of 120° F may shut the burner down at a tank temperature between 110° and 130° F.
The heater will consistently shut off at this same temperature. For this same reason, water temperature may drop
15° F - 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.
Water Temperature Time to Produce 2nd & 3rd
Degree Burns on Adult Skin
160°F (71°C)
About 1/2 second
150°F (66°C) About 1-1/2 seconds
140°F (60°C) Less than 5 seconds
130°F (54°C) About 30 seconds
120°F (49°C) More than 5 minutes
80°F (27°C) - - - - - - - - - - - - - - - -
Gas Control Knob
On|Pilot|Off
Gas Control Knob
Off|Pilot|On
Robertshaw®
Gas Control Valve/
Thermostat
White-Rodgers®
Gas Control Valve/
Thermostat
120°F Mark
Water
Temperature
Dial
130°F
140°F
150°F
130°F
140°F
150°F
Reset Button
Note: Temperature marks noted above are approximate and may vary due to various factors.
BASIC INSTALLATION & OPERATION
Figure 6
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