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MODU-FIRE® FORCED DRAFT
Gas-Fired Boiler Maintenance
Low Air
CAUTION The air switch has been factory set and
should not be adjusted in the field.
The “Low Air” indicator illuminates if the air flow
switch detects low air flow through the boiler.
An extended low air indication does not mean that
the low air switch is defective.
• Check that blower is electrically connected to
the inverter.
• Check that the burner is clean (refer to Section
5.2).
• Check for obstructions in the vent.
• Check for obstructions in the air inlet.
Vent Pressure
In the event of the vent having too much pressure,
the High Exhaust Back Pressure Switch (HEBPS)
will trip and shut down the boiler. This condition
will automatically recycle, so the boiler will try to
relight. The vent and heat exchanger should be
checked for obstructions and cleaned.
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
which de-energizes all outputs from the programmer
except Terminal A, which is connected to the
"Flame Failure" indicator. The Red alarm light will
light up. A manual reset of the programmer (located
inside the control panel) is required and the boiler
power switch should be cycled off and on.
Flame Failure
In the event of a main flame failure during a firing
period, the main gas control valve is de-energized
and the programmer immediately goes into "lockout"
mode. If flame failure occurs and the indicator is
illuminated, the programmer must be manually reset.
All Limit Points Alarm (ALPA)
When there has been a call for heat for greater than 5
minutes and the burner has not advanced to main
flame the all limit points alarm (ALPA) is triggered.
This removes power to terminal 6 of the combustion
control shutting down the burner. The ALARM re-
lay (R7) on the front panel energizes, illuminating
the amber LED. To reset the ALPA you must press
and hold the red inverter reset button until the R7
indicator light goes out.
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