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RESIDENTIAL GAS, NON POWER VENTED, WATER HEATER
SERVICE HANDBOOK
State Water Heater Technical Training Department
© 2004 Ashland city, TN
19
SERVICE:
There is no routine service associated with the TCO. The standard thermocouple millivolt output
checks described in this service handbook still apply. Millivolt readings indicate that the TCO is
closed. An open TCO (within a cool chamber) would indicate that the assembly must be
replaced.
The TCO is an integral part of the thermocouple and not replaceable as a separate item. A pilot
burner assembly must be reinstalled. On repeated calls of no hot water or pilot outage, a
clogged/dirty LDO screen might be the cause and should be checked. Keep in mind this TCO
will shut off the pilot and main burner when activated.
With the different cutoff temperature set-points of TCO devices for different model water
heaters, it is important that the correct part is used when replacement of the pilot burner
assembly is necessary.
Possible service issues associated with the Thermal Cut Off switch being opened:
Pilot outage due to increased combustion chamber temperatures below the main burner.
This may open the automatic reset, thermal cut off switch (TCO).
The flame arrestor having contained a flammable vapor ignition. The TCO will open and
the chamber and arrestor should be inspected by a qualified service agent.
ONE PIECE PILOT BURNER ASSEMBLY
C3 Technology models feature a "one piece" pilot burner assembly. There are five main
components that make up this pilot assembly:
1. Thermocouple with integral Thermal Cut Off switch (TCO).
2. Pilot burner w/orifice and tubing
3. Piezo igniter cable
4. Pilot assembly seal/grommet (orange).
5. An inner door gasket (white) will also be included.