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B. Trouble shooting problems where a soft lockout code is displayed. When a soft lockout occurs, the boiler will
shut down and the display will alternate between the number "9" and the letter "b" followed by a two digit
service code. The boiler will automatically restart once the condition that caused the lockout is corrected.
Table 13.3: Soft Lockout Codes Displayed
CODE
b 08
Pressure switch circuit open
MCBA supply sensor detected temperatures in excess
b 18
of 200°F
MCBA return sensor detected temperatures in excess of
b 19
200°F
MCBA is reading a return sensor temperature higher
b 24
than the supply sensor temperature. Condition must be
present for at least 75s for this error code to appear.
b 25
Supply water temperature has risen too quickly
Boiler safety limit, or external limit wired across terminals
b 26
3&4, is open.
b 30
Temperature rise between supply and return is too high.
b 61
Pressure switch circuit closed with fan off
b 65
Fan is not achieving set point speed
52
CONDITION
POSSIBLE CAUSES
• Blockage in intake or vent system.
• Vent and/or intake system not constructed in accordance
with Part VI.
• Blocked or leaking pressure switch tubing
• Heat exchanger or burner blockage
• Terminals exposed to high winds
• Blockage in condensate trap above vent.
• Heating load at time of error was far below the minimum
firing rate of the boiler
• Defective primary pump or no flow in primary loop (Piping
Method 1)
• Control system miswired so that boiler operation is
permitted when no zones are calling
• See possible causes for "b18"
• Flow through boiler reversed
• Sensor wiring reversed
• Flow through boiler reversed. Verify correct piping and
pump orientation.
• No boiler water flow. Verify that system is purged of air
and that appropriate valves are open.
• Sensor wiring reversed.
• Supply or return sensor defective.
• See possible causes for "b18"
• Inadequate boiler water flow. Verify that pump is
operating and that pump and piping are sized per Part
VIII of this manual
• See possible causes for "b18"
• Defective supply sensor.
• Inadequate boiler water flow. Verify that pump is
operating and that pump and piping are sized per Part
VIII of this manual
• Blockage in pressure switch hose
• Pressure switch wires shorted together
• Defective pressure switch
• Loose or miswired fan speed harness (if "b61" error code
is observed while fan is running)
• Loose or incorrect fan speed control connection
• Defective fan
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