Viessmann B2TF Installation And Service Instructions Manual page 54

Commissioning, inspection, maintenance
Checking the diaphragm expansion vessel and system pressure
Fig. 45
Diaphragm expansion vessel valve
A
Note
The expansion vessel can lose some of its charge
pressure over time. When the boiler heats up, the
pressure rises to 2 or 3 bar (0.2 or 0.3 MPa). The
safety valve may also respond and discharge the
excess pressure.
Therefore check the expansion vessel pre-charge
pressure annually.
Check whether the installed expansion vessel is ade-
quate for the system water volume.
Carry out this test on a cold system.
1. Drain the system until "0" is shown on the pressure
indicator.
2. If the pre-charge pressure of the expansion vessel
is lower than the static system pressure: Top up
with nitrogen at the valve of the diaphragm expan-
sion vessel until the pre-charge pressure is 0.1 to
0.2 bar (10 to 20 kPa) higher than the static system
pressure.
54
A
3. Top up with water until the charge pressure of the
cooled system is at least 1.0 bar (0.1 MPa), and is
0.1 to 0.2 bar (10 to 20 kPa) higher than the pre-
charge pressure of the expansion vessel.
Permiss. operating pressure: 3 bar (0.3 MPa)
Note
The expansion vessel is supplied from the factory
with a pre-charge pressure of 0.7 bar.
Do not allow the pre-charge pressure to fall below
this value (boiling noises). This also applies to sin-
gle floor heating systems or attic heating centres
(no static pressure).
Top up with water until the charge pressure is 0.1
to 0.2 bar above the pre-charge pressure.