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21
SERVICE INSTRUCTIONS – SAFETY DEVICES
Figure 13a
BVSS - Troubleshooting Flow Chart
Limit Control (Overheat Switch)
The limit control, mounted on the left inner side panel (when
facing front of unit), will shut off the gas supply to the main
burner in the event of overheating. It is a single pole single
throw switch. The contacts open to shut the electric gas valve
off in the event the unit should overheat. This limit control
should operate only when something is seriously wrong with the
unit. Anytime this control operates, correct the difficulty
immediately or serious damage may result. If the limit control
cuts off the gas supply during normal operation:
1. Make sure deflector blades are open and that there are not
any obstructions in the air inlet or discharge outlet.
2. Check actual input to unit against rated input.
3. Check to be sure motor is operating.
4. On propeller units, check that fan is not loose on motor
shaft. On blower units, check belt and sheave for tightness
or damage.
5. On propeller units, check fan speed against speed on motor
nameplate. On blower units check blower speed against
Performance Data on pages 18 or 19, check for restriction in
ducts and for dirty filters.
6. Check to make sure the venting system is not damaged or
blocked. Also check to be sure unit is venting normally and
that there is not negative pressure in the building adversely
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