I-UDSA-UK (02-19) PN 06 00116 UDSA R3, page 22
The main operating quick opening gas valve is powered through
the thermostat and safety controls. The main control valve is of
the diaphragm type providing regulated gas flow and is preset at
the factory. The gas valve requires no field maintenance except
careful removal of external dirt accumulation and checking of
wiring connections. Instructions for testing pressure settings
are in section 12.
20
OPERATING GAS VALVE
Warning: The operating valve is the prime safety
shutoff. All gas supply lines must be free of dirt or
scale before connecting to the unit to ensure correct
sealing.
Figure 20 : LC1
Figure 21 : LC3
Figure 22 : Location: LC1/LC3
If a limit control needs replacing, use only the factory autho-
rized replacement part for the size of heater.
For approximate limit locations, see Figure 11a.
If it is determined that the pressure switch needs replacing, use
only the factory-authorized replacement part that is designed
for the model and size of heater being serviced.
Figure 19 :
Warning: Never bypass the limit controls, hazardous
conditions could result.
The combustion air pressure switch ensures that proper com-
bustion airflow is available. The switch senses the differential
pressure between the negative pressure in the flue gas collec
-
tor box and the pressure in the control section.
On startup when the heater is cold, the sensing pressure is
at the most negative level, and as the heater and flue system
warm up, the sensing pressure becomes less negative.
If a restriction or excessive flue pipe length causes the sensing
pressure to be below the allowable level, the pressure switch
will shut off the main burner.
DANGER
Safe operation of this unit requires proper venting flow.
Never bypass the combustion air pressure switch or
attempt to operate the unit without the venter operating.
All units are equipped with temperature activated limit controls.
The controls are factory set and non-adjustable. If either set-
point is reached, the corresponding limit control will interrupt
the electric power to the gas valve. These safety devices
provide protection in the case of motor failure or lack of airflow
due to restrictions. (For locations, see Figure 11a.)
21
COMBUSTION AIR PRESSURE
SWITCH
22
LIMIT CONTROLS
Check the complete system at least once a year. Inspection
should include all joints, seams, concentric adapters and the
flue terminal cap. Replace any defective or heavily corroded
parts.
23
FLUE AND COMBUSTION
AIR PIPING
LC1
LC3
