Combustion Chamber With Tco Switch - State Water Heaters GPX Service Handbook

Scalding Risk
A water
can make
hot enough
cause severe burns
instantly, resulting in severe injury or
death. Higher temperatures increase
the risk of scalding, but even at 120°F,
hot water can scald. See Table 2.
Thermostatic mixing valves at each
point of use reduce the risk of scalding.
HONEYWELL ® GAS CONTROL VALVE/THERMOSTAT
GAS CONTROL/TEMPERATURE KNOB
140°F
130°F
120°F
MARK
VAC
STATUS
LIGHT
IGNITER 55°F
TEMPERATURES SHOWN ARE APPROXIMATES AND MAY VARY.
SOME MODELS ARE CERTIFIED FOR 180°F. SEE RATING PLATE.
Figure 3.
Table 2.
Water Time to Produce
Temperature a Serious Burn
120°F (49°C) More than 5 minutes
125°F (52°C) 1½ to 2 minutes
130°F (54°C) About 30 seconds
135°F (57°C) About 10 seconds
140°F (60°C) Less than 5 seconds
145°F (63°C) Less than 3 seconds
150°F (66°C) About 1½ seconds
155°F (68°C) About 1 second
IMPORTANT: Water temperature
in the tank can be higher than the
thermostat setting. Some of the
reasons are:
• Incoming water temperature is
higher than the set point (e.g.,
solar-heated water).
8 • Residential Standard Gas Water Heater Service Handbook
• The water heater and/or pipes
are located in an area with high
heater
ambient temperatures (e.g., an
water
attic). See also "Attic Installations"
to
on page 23.
• Certain usage patterns, such as
short hot water draws or no hot
water use for long periods of
time, can cause the tank water
temperature to rise higher than the
thermostat setting. Modern water
heaters are very well insulated
and retain heat so efficiently that,
under
the tank water temperature can
155°F
150°F
increase over time, particularly
when hot water is not being used.
This "heating" effect can be caused
by the pilot flame itself.
Combus on
with TCO Switch
Combustion air is drawn through the
base-ring filter and flame arrestor and
into the combustion chamber. (See
Figure 5.) Sufficient combustion air is
critical to the operation of the water
heater.
IMPORTANT:
and filter should be inspected and
cleaned during each service call. See
page 18 for instructions.
Also, each water heater covered by
this handbook is equipped with a
resettable TCO switch (thermal switch),
designed to shut off the gas supply in
the event that the water heater has
been exposed to high combustion
chamber temperatures caused by one
of the following events:
• Flammable vapors (e.g., spilled
gasoline)
• Poor combustion caused by a
blocked vent
• Insufficient combustion air.
A resettable
illustrated in Figure 4. Its reset button
certain circumstances,
Chamber
The flame arrestor
thermal switch is
is located in the center of the switch,
directly between the terminals.
IMPORTANT: If the thermal switch has
been tripped, determine the cause
and correct it before returning the
water heater to service. Ensure that
there are no flammable vapors
present. However, a tripped thermal
switch is most likely caused by poor
combustion (e.g., blocked vent or dirty
filter/arrestor).
THERMAL SWITCH (TCO) LOCATION
THERMAL
Figure 4.
FLAME ARRESTOR COMBUSTION CHAMBER
BASE-RING
FILTER
Figure 5.
SWITCH
(TCO)