Caution
The O
2
values at part load must be higher than the O
2
values at
full load.
7.3.4 Basic setting for the gas/air ratio
If the gas/air ratio is out of adjustment, the gas valve unit has a basic
setting. To do this, proceed as follows:
1. Switch off the boiler's electrical connection.
2. Close the gas valve on the boiler.
3. Remove the air inlet flue on the venturi.
4. Unscrew the top nut on the gas valve unit.
5. Disconnect the connector(s) located under the fan.
6. Release the 2 clips holding the fan/mixing elbow unit in place on the
heat exchanger.
7. Remove the fan together with the mixing elbow unit.
8. Turn adjustment screw A on the gas valve unit to modify the position
of the restrictor:
8.1. Turn adjustment screw A until the restrictor is fully closed.
8.2. Turn adjustment screw A anticlockwise. Refer to the table for
the amount of rotations per appliance and gas type.
Tab.53 Adjustment screw A
Gas type G20 (H gas) G30/G31 (butane/
propane)
AMC 15 6 rotations 4 rotations
AMC 25 9 rotations 6 rotations
AMC 25/28 MI 9 rotations 6 rotations
AMC 35 9 rotations 6 rotations
When the appliance does not start directly, turn the adjustment
screw A one extra rotation anticlockwise.
9. Turn adjustment screw B on the gas valve unit to modify the position:
9.1. Turn the adjustment screw B clockwise until it reaches the
stop.
9.2. Turn the adjustment screw B 2 ¼ rotations anticlockwise.
10. Fit all removed parts in the reverse order.
11. Check the gas settings.
For more information, see
Checking/setting combustion, page 72
7.4
Final instructions
1. Remove the measuring equipment.
2. Screw the cap on to the flue gas measuring point.
3. Seal the gas valve unit.
4. Put the front casing back.
5. Heat the central heating system up to approximately 70°C.
6. Switch the boiler off.
7. Vent the central heating system after approx. 10 minutes.
8. Turn on the boiler.
9. Check the water pressure. If necessary, top up the central heating
system.
Fig.74 Gas valve unit
Fig.75 Adjustment screw A
Fig.76 Adjustment screw B
7 Commissioning
7686707 - v.01 - 06092018 AMC 75
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