Modine Manufacturing GAS-FIRED HEATERS BD - Manual (Page 21)

21
SERVICE INSTRUCTIONS – SAFETY DEVICES
Figure 14
BVSS - Troubleshooting Flow Chart
If these changes do not stop the spillage or the installer
chooses not to make changes, a power exhauster is really the
only recommended fix (see bulletin 6-530).
Low ambient installations can also be a cause for extended
spillage. Be aware that in these installations for freeze
protection and/or condensate protection, there is a good
chance that a power exhauster will be necessary.
In instances where the blocked vent safety switch trips
repeatedly, refer to Figure 14.
After the vent system has been changed, or if no blockage or
damage is found in the vent system, the blocked vent switch
may be reset. To reset the blocked vent switch, depress the
reset button located on the switch in the top of the unit.
With the switch reset, turn on the electric and gas supply to the
unit heater and restart the unit. Carefully observe the operation
of the unit to assure that it is operating correctly. If the block
vent switch does not allow the unit to function, or trips after the
unit has operated for a period of time, call a qualified service
agency to service the equipment. Do not attempt to bypass the
blocked vent safety switch with a switch. Do not attempt to
replace a defective blocked vent safety switch with a switch
other than that supplied by the unit heater manufacturer.
Is vent blocked or restricted?
Remove restriction Is there spillage after 5 minutes? (see note 1)
Is there a negative pressure in building? (see note 2) Replace blocked vent switch;
Does switch still trip?
OK Is vent in compliance
with NFGC?
Can negative pressure
be corrected?
Correct vent Install
power vent
accessory
Correct
negative
pressure
Is unit overfired?
Reduce input Can one or more of the following be done?
• Lengthen vertical vent run
• Insulate vent
• Use larger diameter vent
• Use less restrictive weather cap
OK Install power
exhauster accessory
Does unit still trip? Install power vent
accessory
YES
YES
YES
YES YES
YES
YES
YES
YES
NO NO
NO NO
NO
NO
NO
NO
NO
To determine spillage, place lit match
stick (6" - 8" match stick if possible) 2" - 3"
into diverter relief opening and determine
direction of the flame (or direction of
smoke if flame goes out). If flame or
smoke comes back at you, there is
spillage. The flame or smoke should be
pulled in.
One indication of negative pressure is
that outside doors tend to swing toward
inside of building. Note 1:
Note 2:
Heater Parts from ACF Greenhouses