Camus Hydronics Valiant FT VA0080, Manual

Page: 22 / 79

15
AIR PRESSURE SWITCH, BLOCKED FLUE &
CONDENSATE SWITCH
The air proving switch and blocked venting switch are wired
in series. When the error on the control shows “Air Switch
Open”, it could be a result of these switches. A minimum
pressure across the differential air switch proves the
combustion air fan. A failure of this switch to close could be
due to several factors such as, sensing line broken or loose
fitting, blocked vent, steady high wind condition or an
incorrectly set switch.
The Blocked Flue & Condensate switch is mainly due to a
blocked air intake or vent condition. When the blocked flue
switch has tripped, check the venting and/or air intake
piping for obstructions before placing the unit into operation.
Power must be shut off to the boiler and gas supply to the
appliance must be closed before attempting to investigate
reason for blocked flue condition.
3.0 COMBUSTION COMPONENTS
Figure 20: Combustion Components Assembly
3.1 AIR/ GAS RATIO CONTROL VALVE
Figure 21: Negative Pressure Control Valve
Operation of the gas valve in combination with the
combustion air fan allows the burner input rate to vary from
10% to 100%. These utilize a 1:1 ratio dual seat negative
pressure gas valve. The gas valve adjusts fuel supply
according to negative pressure generated by the
combustion fan. The valve is dual seat and serves as a
safety shut-off. The inlet gas supply pressure must be
maintained within the specified minimum and maximum
pressures (a reduction of up to 30% is permitted in the inlet
gas pressure between light-off and full fire conditions).
3.2 GAS PRESSURE SWITCHES (Optional)
Gas pressure switches prevent the burner from being
activated if pressure is outside certain ranges. Each switch
is a physical manual reset device, requiring physical
depression of the reset button if it is not closed prior to
burner start or during burner operation.
3.2.1 Low Gas Pressure
A low gas pressure switch monitors the minimum incoming
gas supply pressure supplied to the gas train. If gas
pressure upstream of the valve(s) falls below the minimum
setting of the pressure switch, the switch will open and the
appliance will shut down. An open gas pressure switch
alarm will be shown on the display.
3.2.2 High Gas Pressure
High gas pressure switches may be ordered to comply with
CSD-1 code. These will either be integrated in to the gas
train. If gas pressure downstream of the gas valve(s)
exceeds the maximum setting of the pressure switch, the
switch will open and the appliance will shut down.
3.3 AIR PRESSURE SWITCHES
3.3.1 Blocked Flue Switch
All models use a normally closed blocked flue switch to shut
down the appliance under conditions of blockage of the air
intake or the flue outlet.
3.3.2 Low Air Switch
The low air switch is closed by operation of the combustion
air blower, to confirm that there is air flow present. This
switch is adjustable but typically does not need to be altered
from factory settings. Once this switch is closed the unit
initiates the pre-purge counter. If this switch opens during
operation the unit will lock-out.