A.O. Smith TC-099 User Manual

AOS WPC - Tech Training

58 of 72

Ashland City, TN © 2007

Servicing should only be performed by a Qualified Service Agent

Flame or ignition failure.
Error message displayed after 1 or 3 losses of flame 
or after 1 or 3 failed trials for ignition. EMC 5000 
control system will lock-out after 1 or 3 trials 
depending on the SW1 #2 dip switch setting on the 
MCB circuit board. (see page 30)

When performing any troubleshooting steps outlined 
in this service manual always consider the wiring 
and connectors between components. Perform a 
close visual inspection of all wiring and connectors 
to a given component before replacement. 

Ensure wires were stripped before being crimped in 
a wire connector, ensure wires are crimped tightly in 
their connectors, ensure connection pins in sockets 
and plugs are not damaged or worn, ensure plugs 
and sockets are mating properly and providing good 
contact.

Failure to perform this critical step or failing to 
perform this step thoroughly often results in 
needless down time, unnecessary parts 
replacement, and customer dissatisfaction.

•

Check igniter amperage during igniter warm up 
period. If amp draw is less than 3.0 amps 
replace the igniter.

•

Ensure the 1/8” steel sensing tube that connects 
between the gas valve (near the low fire adjust-
ment screw cap) and the Venturi assembly is 
not clogged or damaged and properly con-
nected at both ends. If the tube is kinked or 
damaged - replace the tube. Remove the steel 
tube and blow through it to ensure it is not 
clogged. Reinstall and tighten the compression 
fittings tightly at both ends.

•

Ensure the 24 VAC gas valve is being energized 
during ignition:

If the burner is failing to ignite when viewed 
through the view port on the top of the heat 
exchanger - check for 24 VAC between pins 1 & 
2 of the J19 socket on the MCB (page 28) at the 
end of the igniter warm up period. If 24 VAC is 
present - check all wiring between the J19 
socket and the gas valve. Check the J19 socket/
plug pins for wear or damage. Check the ground 
(green) wire from gas valve coil to the ground 
connections in the junction box on the boiler - 
repair/replace anything worn or damaged.

If 24 VAC is not present between pins 1 & 2 of 
the J19 socket on the MCB - call the A. O. Smith 
technical information center for further assis-
tance at 800 527-1953.