Reznor EXUB Unit Installation Manual - Manual (Page 7)

7
Heat Exchanger Replacement
The heat exchanger has been air evacuated, fluid filled, and sealed at factory and is not field repairable. Replacement heat
exchangers are available from the factory and are inspected and electrically tested for correct heat output and proper
operation of the high-limits.
1. Explosion/Electric Shock Hazard. Disconnect heater from power supply or fuse box before opening enclosures or
servicing heater. Lock the switch in the “OFF” (open) position and/or tag the switch to prevent unexpected power appli-
cation.
2. To prevent burn hazard, be sure heat exchanger and fluid has been allowed to cool before proceeding.
3. Remove cabinet bottom panel, element housing cover, element enclosure cover, & control enclosure cover.
4. From the control enclosure, disconnect two high-limit wires from printed circuit board terminal block marked 3 & 4 and
disconnect three output heating element wires from contactor terminals marked T1, T2, & T3.
5. Slightly loosen all cabinet bolts and louver screws to prevent heat exchanger from binding.
6. The heat exchanger is secured by three 1/4 in. bolts on the right-side cabinet panel (when facing front of heater) and
one 1/4 in. bolt located on the left side of heater. On 5 - 10kW models the left-side bolt is located at the top right-hand
foot of control enclosure. On 15 - 35kW models the left-side bolt is located above the control enclosure. With an assis-
tant supporting the weight of the heat exchanger remove these 4 bolts. Carefully lower the heat exchanger from the
cabinet.
7. Reverse the above procedure when installing a new heat exchanger.
Temperature High-Limit Replacement
This heat-exchanger includes one automatic reset & one manual reset temperature high-limit that are wired in series. The
automatic reset high-limit is rated for 100,000 cycles and is for a temporary failure condition. Continuous nuisance tripping
of the automatic reset is generally not the fault of the high-limit but is usually caused by incorrect operating voltage, blocked
air inlet or outlet, fan/motor malfunction, high ambient temperatures, excessively dirty heat exchanger or leaking heat ex-
changer. Care should be taken to determine the exact reason that the automatic reset high-limit control tripped so
the problem can be resolved immediately. The automatic reset high-limit normally fails in the open position, however, it
can also fail closed.
If the automatic reset fails in the open position the heater will not function and the high-limit should be replaced. The
occurrence of the manual reset high-limit control to trip is an abnormal condition and indicates that the automatic
reset high-limit has failed in the closed position. If this occurs remove the heater from service immediately and
replace the automatic reset high-limit. Determine the exact reason that the automatic reset high-limit control
tripped so the problem can be resolved immediately. If the manual reset high-limit shuts down the heater it will have to
be reset by pressing on the small reset button protruding from the center of the high-limit device.
1. De-energize the heater electrical supply circuit.
2. Remove element housing cover, and element enclosure cover.
3. Remove spade connection from the automatic reset high limit lugs.
4. Remove automatic reset high-limit assembly by unscrewing, and clean the inside of the thermowell. A clean thermowell
ensures good thermal contact.
5. Replace high-limit with a factory supplied unit only. Apply a small drop of heat sink conductive cement around the base
of the high-limit, but not on the threads, and screw into thermowell. Attach spades to automatic reset high-limit .
6. Replace control enclosure cover, element housing cover, and element enclosure cover.
7. Energize the heater electrical supply circuit and let run for 15 minutes to reach a stable operating temperature.
8. If heater operation appears to be normal, place unit into service.
— WARNING! —
Heater is to be serviced only by qualified electrician experienced with hazardous location equipment.
Explosion/Electric Shock Hazard. Disconnect heater from power supply or fuse box before opening
enclosures or servicing heater. Lock the switch in the “OFF” (open) position and/or tag the switch to prevent
unexpected power application.
— Repair and Replacement —