Operating instructions

1104UESAGBEN, page 18/31
8. CONTROLS
8.1 Thermostats
Use either an optional thermostat (1 stage room thermostat, 2 stage clock thermo-
stat, Smartcom control panel or wireless digital thermostat) available with the heater
or a fi eld supplied 230V thermostat. Install them according to the manufacturer’s
instructions, paying full attention to the requirements regarding the thermostat loca-
tion (see section 7.2).
Important : never use a line voltage isolating switch as a means to operate the oper-
ate the heater.
8.2 Gas valve
The main gas valve is powered through the thermostat and safety controls. The
gas valve provides regulated gas fl ow and is preset at the factory. The gas valve
requires no fi eld maintenance except careful removal of external dirt accumulation
and checking of wiring connections. Instructions for testing pressure settings are
in section 6.
WARNING
The main gas 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.
8.3 Safety controls
8.3.1 Combustion air pressure switch
The combustion air pressure switch ensures that proper combustion airfl ow is
available. The switch senses the differential pressure between the negative pres-
sure in the fl ue gas collector box and the pressure in the control section. (For
switch location, see fi gure 16a).
On startup when the heater is cold, the sensing pressure is at the most negative
level, and as the heater and fl ue system warm up, the sensing pressure becomes
less negative.
If a restriction or excessive fl ue pipe length causes the sensing pressure to be be-
low the allowable level, the pressure switch will shut off the main burner.
Figure 12
Combustion air
pressure switch
If it is determined that the
pressure switch needs
replacing, use only the
factory-authorised re-
placement part that is
designed for the model
and size of heater being
serviced.
Table 7
Set points OFF
UESA Set point Off (Pa)
035 238
055 388
083 300
102 450