MFTCW and MFTHW - Error 72

MFTCW and MFTHW - Error 72

Error 72 is a SOFT LOCKOUT defined as Flame Signal Detected Before Ignition.

FYI - THE NUMBERED BLUE BOXES BELOW CORRELATE TO A SPOT ON THE FLOW CHART ABOVE

(1) Explanation of Error 72 - Soft Lockout

Error 72 occurs when the flame detector senses flame PRIOR to the burner firing. 
The key cause seen has been debris on the top of the burner plate "glowing"  that has entered from the intake air piping. 
Another cause can be "room light " being picked up by the flame detector with the boilers front cover being off the boiler during operation. 

(2)  Debris Entering Into Intake Piping 

  1. Improperly installed air intake piping where debris can easily be "sucked" into the burner should be corrected immediately. 
  2. Intake piping near or around clothes dryer vents should be relocated.
  3. Intake piping installed too low to the ground can easily "suck" leaves, dirt, wood chips, mulch into the burner. (See Attachments).
  4. Assure that the termination (outside) of the air intake piping has a bird screen on it 
  5. Shavings , debris from PVC pipe (when used on air intake piping ) is a very common cause of error 72 ! Assure all shavings , cuts are reamed, scraped and cleaned thoroughly from PVC piping prior to installation. 
  6. Removal of the burner plate for inspection, cleaning or replacement might be necessary if debris, PVC shavings, etc. have entered the intake piping and now onto the burner plate. ( A video of burner removal is below ) .

(3) Testing and Troubleshooting the Optical Flame Sensor

  1. Using a multi meter the optical flame sensor can be tested. (A video of Optical Flame Sensing is below) 
  2. A voltage of LESS than 2.5VDC is normal PRIOR to ignition (looking into a dark inactive chamber) .
  3. A voltage of MORE than 2.5VDC is normal AFTER ignition (active fire in chamber) . 
  4. If either of these voltages are incorrect, replace optical flame sensor.

A proper COMBUSTION ANALYSIS and ADJUSTMENT is a MUST after burner removal. See Video below.



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