11.3.6 Checking the air box
1. Check the air box for soiling.
2. Clean the dirty air box using a vacuum cleaner. Do this from the
connection opening for the air supply hose.
Important
If the air box is dirty, the following components must also be
dismantled and blown clean:
Non-return valve
Venturi
Fan
11.3.7 Checking the air pressure differential switch
1. Switch off the boiler.
2. Remove any dirt from all the connection points for hoses and the air
pressure differential switch.
3. Check the condition and tightness of the hoses of the air pressure
differential switch.
Replace the hoses if necessary.
4. Disconnect the silicon hose from the + side (P1) of the air pressure
differential switch.
5. Connect a hose to the + side of the air pressure differential switch.
6. Take a T piece and connect it as follows:
6.1. Connect one end of the T piece to the hose from the + side of
the air pressure differential switch.
6.2. Connect one end of the T piece to a large plastic syringe.
6.3. Connect the other end of the T piece to a pressure gauge.
7. Switch on the boiler.
8. Push the syringe in very slowly until error code E.04.08 appears on
the display.
9. Check the pressure indicated by the pressure gauge at that point. This
is the switch pressure.
A switch pressure between 5.5 and 6.5 mbar is good. A lower or
higher switch pressure indicates a problem with the air pressure
differential switch.
Fig.113 Air box
AD-0000536-01
1
2
Fig.114 Positive (+) side of the air pressure
differential switch
AD-3001570-01
X mbar
(+)
P
2
(-)
P
1
(+)
5
4
6
9
8
11 Maintenance
150
C 340 / C 640
7762666 - v.02 - 29092020
