17
Bottom tube from venturi to P1 on air pressure switch (right hand side) provides positive
pressure to the air pressure switch.
To check for correct operation of the venturi place a manometer on one of test points
located on the top of the boiler. With the fan running note the reading on the manometer
and then take a 2
nd
reading from the other test point. The difference between the two
readings is the differential pressure.
Minimum differential pressure to activate the switch is 1.4mb.
Switch will deactivate as the differential pressure falls below 0.9 mb
Readings for a 600 mm horizontal flue in still air are:
REAR TEST POINT + 2mb
= 3.9 mb
FRONT TEST POINT – 1.9mb
N.B. Contamination of the venturi by insects will prevent sufficient airflow to produce the
required pressure drop and will cause the boiler to lock out. Please see section 4 (fault
code 1) for more details.
13. ROOM THERMOSTAT CONNECTOR
Located within the PCB electronics box is the room thermostat connector block. Access to
the connector is via the small removable panel on the under side of the electronics box.
Voltage is fed from the PCB J4 22V dc (left hand black) and returns to the PCB J4 right
hand black via the time clock terminals 4 and 1. Voltage reduces to 12.5V dc when clock
and thermostat contacts are both closed.
N.B. Loose or poorly connected room thermostat link wires at the connector block will
cause problems with the heating demand, and will not be displayed as a fault code as the
failure is not a safety related mater.
15. MODULATING GAS SOLENOID VALVE
This is located on the main gas valve. It adjusts the burner pressure in proportion to the
temperature selected at the control panel, and the real time temperature values at the
thermistors.
Voltage is supplied from the PCB from J6 (lower 2 whites) as voltage to the solenoid
increases, the burner pressure will increase also. The voltage is measured in parallel at
the terminals at the solenoid.
Nominal figures are;
0.8V dc at minimum burner pressure (4.0 mb)
12.5V dc at maximum burner pressure (35.0 mb)
6.5V dc at ignition pressure (8.0 mb)
Resistance value of the coil with leads disconnected = 78 Ohms
The ignition pressure cuts as soon as the ionisation electrode detects that the main burner
flame has established.
To Next Page
Loading...
