Harsco Industrial MODU-FIRE FORCED DRAFT N750 Installation & Owner's Manual page 38

MODU-FIRE® Forced Draft Gas-Fired Boiler
When AIR SWITCH NOT OPEN is shown on the display, check that the air switch is open when the fan is off. Check
that there is no air flow through the boiler when the fan is off.
When AIR SWITCH NOT CLOSE is shown on the display, check that the air switch is closed when the fan is running.
If the air switch does not close within 5 minutes during purge, the boiler locks out. Check that the burner is clean and
that there are no obstructions to airflow in the intake or exhaust ducts.
5.6.7 Vent Pressure
BLOCKED FLUE indicates that the high exhaust back pressure switch has tripped. This may be caused by a blocked
stack, a blocked air inlet, or a blocked condensate system. When the blockage is removed, the boiler will automatical-
ly restart.
5.6.8 Ignition Failure
In the event the flame is not detected by the UV scanner during the 4 second trial-for-ignition period (Step 9), the gas
valve and spark ignition are de-energized. At this time a safety lockout occurs. A manual reset of the programmer
(located inside the control panel) is required.
5.6.9 Flame Failure
In the event of a flame failure, the main fuel valves are de-energized and a manual reset lockout occurs. IGNITION
ERROR or FLAME ERROR is shown on the display. The cause of flame failure must be diagnosed and repaired be-
fore the control is reset.
When IGNITION ERROR is shown on the display, the boiler has not lit during a trial for ignition. Check that the spark,
electrode, ignition wire, and gas valve are functioning properly.
When FLAME ERROR is shown on the display, the boiler has lost the flame during run. Check that the combustion is
setup properly, the gas pressure is correct, as well as other combustion parameters.
5.6.10 Flame Error
LATE FLAME and EARLY FLAME and FALSE FLAME.
These errors signify flame error. This may be caused
by a failed or leaky gas valve or a flame detector malfunction. If gas valve leakage is suspected, the unit must be iso-
lated by turning off the main gas supply line. Qualified and knowledgeable service personnel must be called to eva-
luate and repair/replace the failed parts.
A comprehensive listing of the locking and blocking error codes is provided below.
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