Fulton Vertical Tubeless (FT-A) Thermal Fluid (hot oil) Heater - Manual (Page 69)

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SECTION 4
FTA-IOM-2013-0227
MAINTENANCE
4-9
pressure switch.
AIR SWITCH
All A-model heaters have an Air Switch. This is a normally
open switch that closes with proper burner fan outlet
pressure. This switch is generally a diaphragm type switch.
The Air Switch is a safety device that proves that there is an
adequate pressure and volume of make up air for proper
combustion and mixing. There is no manual reset on the air
switch itself to indicate a trip. The most likely time of an air
switch trip is at low fi re purge or low fi re. If this switch trips, it
is generally one of the issues indicated in Table 10-F.
AIR FILTER SWITCH
A-model heaters with an air fi lter box or ducted supply air
have an Air Filter Switch. This is a normally closed switch that
opens on too high of a suction pressure at the burner fan
inlet. This switch is generally a diaphragm type switch.
The Air Filter Switch is a safety device that proves that there is
not too negative of a pressure at the combustion blower inlet.
This switch is only used on units that have a built in air box for
use as a duct connection or air fi ltering device.
There is no manual reset on the air fi lter switch itself to
indicate a trip. The most likely time of an air fi lter switch trip is
at high fi re purge or high fi re. If this switch trips, it is generally
one of the issues indicated in Table 10-G.
AUX. BLOWER MOTOR STARTER
All A-model heaters use an auxiliary set of contacts on their
blower motor starter to prove that the burner motor is
latched on. This is a normally open set of contacts mounted
on or built in to the blower motor starter. The Auxiliary Blower
Motor Contacts are a safety device that proves that the blower
motor starter is latched in. These contacts work in redundancy
to the air switch to prove that there is proper makeup air.
There is no manual reset on the auxiliary contacts themselves
to indicate a trip. If the contacts do not make, it is generally
one of the issues indicated in Table 10-H.
HIGH TEMP. LIMIT
All thermal fl uid heaters have at least one High Temperature
Limit. The high temperature limit(s) is/are normally closed
switch(es) that break on a temperature rise over set point.
The switch may be either a solid state controller or a bulb and
capillary type switch. The High Temperature Limit is a safety
device that protects from excessively high temperatures.
Solid-state high temperature limits will have a manual reset.
Bulb and capillary type limits will not have a manual reset.
If this/these switch(es) trips, it is generally one of the issues
indicated in Table 10-I.
HIGH GAS PRESSURE SWITCH
All gas-fi red modulating thermal fl uid heaters may have a
High Gas Pressure Switch. This is a normally closed diaphragm
switch that opens on a pressure increase over set point. The
High Gas Pressure Switch is a safety device that protects
the burner from receiving too high of a gas pressure. The
switch senses this pressure downstream of the last gas valve,
upstream of the modulation valve on units that modulate.
This switch is most likely to trip at low fi re. If this switch trips, it
is generally one of the issues indicated in Table 10-J.
LOW GAS PRESSURE SWITCH
All gas-fi red modulating thermal fl uid heaters may have a
Low Gas Pressure Switch. This is a normally closed diaphragm
switch that opens on a pressure decrease below set point.
The Low Gas Pressure Switch is a safety device that protects
the burner from receiving too low of a gas pressure. The
switch senses this pressure just downstream of the gas
regulator. This switch will most likely trip at high fi re. If this
switch trips, it is generally one of the issues indicated in Table
10-K.
LOW OIL PRESSURE SWITCH
All oil fi red on/off thermal fl uid heaters may have a Low Oil
Pressure Switch. This is a normally closed diaphragm switch
that opens on a pressure decrease below set point. The Low
Oil Pressure Switch is a safety device that protects the burner
from receiving too low of an oil pressure. The switch senses
this pressure just downstream of the oil pump. If this switch
trips, it is generally one of the issues indicated in Table 10-L.
PILOT FLAME FAILURE
A Pilot Flame Failure is a fl ame failure that occurs when the
unit is trying to establish an adequate fl ame signal. Solid-state
controllers indicate a Pilot Flame Failure by showing as a fault
code either Fault 28 for Honeywell 7800 series controllers.
Flame Failure PTFI on Fireye E110 series controllers or Fault
9 on Fireye Nexus controls. For electro-mechanical controls,
you need to witness when the failure occurs. A Pilot Flame
Failure indicates that either a strong enough pilot fl ame
was not generated or the means of sensing the pilot fl ame
strength has failed. All gas fi red units have a gas pilot. Oil fi red
units may be 2-stage, in which the 1st stage to light would be
considered the pilot, or may have a gas pilot. In either case,
during the pilot proving period, the fl ame programmer must
sense a strong enough fl ame to initiate the opening of the
main valves. See Table 10-M.