Unit Function
HDS Middle Range / HDS Premium Range
Page 44 / 127
Service Manual 04.2008
2.18 Burner fan with fuel pump
Fuel pump with coupling
6
1
2
3
4
Impeller with fuel pump removed
Fuel pump
The fuel pump (2) is directly connected to the
motor shaft via the coupling (6) and the impeller
(7). It pumps fuel from the tank and back again
via the return, even during cold water operation.
This helps to lubricate the gear pump.
During hot water operation the attached soleno-
id valve (5) opens and part of the fuel passes
through the fuel nozzle into the burner where it is
ignited.
The fuel pressure is adjusted using the central
adjusting screw (3).
The fuel pump is blocked by dry running. The
coupling acts as a pressure-relief joint.
Burner fan
The fan supplies the burner with combustion air.
The air flap is used to adjust the air volume to
optimum combustion values. The impeller (7) is
mounted on the motor shaft with 2 keys.
Removing the fuel pump
– Loosen the pressure line from the connection
(3).
– Undo the fuel pump retaining screw (1).
– Remove the fuel pump (2).
8
2
6
7
9
5
1 Retaining screw, fuel pump
2 Fuel pump
3 Adjustment, fuel pressure
4 Connection, pressure line to the burner
5 Solenoid valve, fuel pump
6 Coupling
7 Impeller
8 Retaining screw, impeller fan wheel
9 Retaining screw, fan cover, inner section
(4x)