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  MACH®  Series
 
Gas-Fired Boiler 
Maintenance 
 
 
Page  33 
Loss of Water Level 
The low water switch opens when there is insufficient 
water level in the boiler.  E 12 is shown on the display, 
and burner operation is interrupted.  When the correct 
water level is re-established, pushing the reset button 
will return the sequence to Step 5, provided that the 
other limits are satisfied. 
 
Low Gas Pressure 
The low gas pressure switch opens when there is (or 
has been) insufficient gas pressure available for proper 
operation of the boiler; E 12 is shown on the display, 
and burner operation is interrupted.  If a gas-supply 
shut-off valve is closed for any reason, a low gas 
condition will result. 
When gas pressure is restored, E 12 will remain on the 
display panel, and the boiler will remain locked out 
until the front panel reset button is pressed. 
Once the control is reset, the sequence returns to Step 
5, provided that the other limits are satisfied. 
 
High Gas Pressure 
The high gas pressure switch opens when there is (or 
has been) excessive gas pressure for the proper 
operation of the boiler.  An E 12 service code is 
displayed and the burner operation is interrupted. 
When proper gas pressure is restored, E 12 remains on 
the display with the boiler locked out until the front 
display panel reset button is pressed. 
 
High Water Temperature 
When the boiler water has exceeded both the operating 
and high-limit temperature the high limit switch opens, 
and E 12 is shown on the display.  When the water 
temperature falls below the high-limit temperature, the 
boiler will remain locked out until the switch is 
manually reset and the front panel reset button is 
pressed.  Once the switch, and the front panel are reset, 
the sequence returns to Step 5, provided that the other 
limits are satisfied. 
 
Low Air 
If the display panel indicates E 08 this indicates 
insufficient airflow through the burner.  Check that the 
burner is clean ("Cleaning the Burner," Section 5.2) 
and that there are no obstructions to airflow in the 
intake or exhaust ducts.  A low air indication does not 
necessarily mean that the low air switch is defective.  
 
Air Switch Closed 
If the display panel indicates B 61 this indicates the air 
pressure switch did not open when the blower was shut 
off.  Check that there is no air flow through the boiler 
when the fan is off.  If there is no hidden source of air 
flow, replace the switch.   
 
Flame Failure 
In the event of a flame failure during a firing period or 
a trial for ignition, the main fuel valves are de-
energized and a manual reset lockout occurs.  After the 
spark ignition is re-energized, the 3 second trial-for-
ignition begins again.  If flame failure occurs during a 
trail-for-ignition, a safety lockout occurs.  The display 
will indicate E 02.  If flame failure occurs and an 
service code is displayed, the combustion control must 
be manually reset. 
E 00 signifies a leaky gas valve.  In the event of a false 
flame signal E 00 fault code is indicated.  This fault 
code could indicate a gas valve failure or leakage of 
the gas valve.  If gas valve leakage is suspected, the 
unit must be isolated by turning off the main gas 
supply line until the gas valve is replaced.