MACH® Series
Gas-Fired Boiler
Maintenance
Page 35
5.5.2 Auto-reset Service Codes
Code Lockout
Description
b 08
Air pressure switch open.
The air pressure switch failed to close to indicate sufficient air flow to start the boiler.
b 24
Switched inlet / outlet.
The inlet water temperature has been more than 18° F above the outlet for more than
75 seconds.
b 25
Outlet temp rapid change.
The outlet water temperature is increasing too fast. Indicates a low flow condition.
b 26
High exhaust back pressure.
The high exhaust back pressure switch is tripped indicating a blocked stack, inlet, or
condensate system or external interlock jumper is open.
b 30
Max delta T.
The temperature rise across the heat exchanger is greater than maximum allowed,
indicating insufficient flow.
b 40
Flue sensor open.
The flue gas temperature sensor is indicating an open circuit.
b 52
High flue temp.
The flue temperature has exceeded the maximum allowable setting.
b 61
Air pressure switch closed.
The air pressure switch failed to open prior to starting the blower.
b 65
Fan speed incorrect.
The fan is being directed to a higher speed than it is achieving.
