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OPERATION AND SERVICE
HOW IT WORKS
This section of the Service Handbook will cover operation, common service procedures and water heater
construction. The water heater covered in this Service Handbook has a helical shaped coil heat exchanger
that is submerged in the storage tank. These water heaters use a top mounted down fired radial design
Burner. This is a forced draft burner; hot burning gases are forced through the heat exchanger under pressure
and exit through the exhaust/vent connection located at the bottom of the water heater.
Starting at the top air and fuel gas are drawn in by the Combustion Blower and Venturi. Flue gases and are
forced through the helical shaped heat exchanger by the Combustion Blower and out through the exhaust/
vent outlet.
COMBUSTION BLOWER
The Combustion Blower is an assembly that includes the blower housing, blower motor and an electronic
speed control. The Combustion Blower is controlled by the CCB (Central Control Board) and is powered by
a 3 pin wiring plug receiving 120 VAC from the Junction Box.
The CCB sends a signal from the J5 socket to a 5 pin wiring socket on the blower. The signal is an electronic
instruction to start, stop, and control blower speed.
The Combustion Blower runs at higher speeds during the Pre/Post Purge operating states and runs at a
lower speed during the Trial For Ignition operating state. The Igniter Status icon is displayed on the UIM
during the Trial For Ignition operating state.
MODULATION
The water heaters covered by this Service Handbook are capable of modulating their firing rate. The CCB
monitors the water temperature in the tank and regulates the firing rate to achieve the target temperature
setpoint. The firing rate is dictated by the hot water draw, proximity to the tank temperature setpoint, and
various other temperature limitations. Ramping up and down of the blower speed is considered normal
operation of the water heater.
CONDENSATE PREVENTION ALGORITHM
In order to prevent condensate build-up in the heat exchanger the water heaters covered by this Service
Handbook incorporate a water temperature based modulation algorithm. The amount the blower will modulate
is dependent upon the water temperature at the lower temperature probe. If the water temperature at the
lower temperature probe is above a specified temperature setpoint the blower will fully modulate. If the water
temperature at the lower temperature probe is below a specified temperature setpoint the blower will only
modulate to the heating speed rpm value of the model with the lowest BTU/input rating of that model family.
Example: a natural gas SUF 100250 with a heating speed rpm value of 8700 will only modulate to the SUF
100150 heating speed rpm of 5185. See chart on page 39 for the blower speed RPM and lower temperature
probe setting values.
Servicing should only be performed by a Qualified Service Technician
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