A. O. Smith Water Products Company
Service Handbook
Irving, Texas 2000
©
Training Department
13
Note: If the lower temperature probe is defective or unplugged, display will show upper tank
temperature. Heater may fire but stack.
If upper high limit/tank temp. thermistor is defective or disconnected, cycling power off then on
displays will be: 00, 120, 12, water temp at lower probe, flashing "04" code.
BTH Sequence of Operation
Gas Valve Opens
Power Off
Power On
Call for heat (Temp.
setting less diff.)
Blower Prepurge
20 Seconds
HSI is Energized
Blower speed
reduces BTH 250
only
Igniter
warm-up period
Blower to Full RPM
BTH-250 only
7.5 Sec Trial
for ignition
Blower Prover
Closes at .45"
Positive Press
BTH 120 and 250
Only
Low Supply Gas
Pressure
Switch NC 4.3"
w.c. gas
press. to close
If ECO is closed low
gas pressure switch
is closed
(120 & 250
models only)
Blocked Outlet-NC
Opens at 2.5"
Positive Press
NO
Flame Rod Does
Not Prove Flame
30 Second
Purge
Retry-Max
3 times
YES
Flame Rod Senses
Flame .7 microamp
minimum
Gas Valve Closes
30 Sec Post Purge
Tank Water Heated
to Set Point
If reset is pushed
and released while
this is displayed, the
board will do an
operational self
check.
Pushing the reset at
this time will display
tank temp. setting.
Push once and hold
to increase setting.
Push twice and hold
to decrease settings
110°-180°
Display "00"
Supply Volts
"120"
Weighted Average
Tank Termpature
Bottom vs Top
Draft Prover
Switches to
Proper State
Blocked Inlet-NC
Opens .75" wc
Neg. Press
Temperature
Offset 12%
Display Sequence
Pressure Switch Information
Display Failure Code
Summary of Contents for BTH 120
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