Viessmann B2HF - Checking the flow limiter (only for gas condensing combi boiler); Checking the expansion vessel and system pressure

59
A
2.
4.
3.
Fig. 46
1. Drain the boiler on the DHW side.
2. Remove the spring clip.
3. Remove the DHW flow sensor.
4.
Check flow limiter
A
. Replace in case of exces-
sive scaling or damage. Reinsert.
5. Mount DHW flow sensor with new gaskets.
Danger
Risk of electric shock from escaping heating
water or DHW.
Check all water side connections for tight-
ness.
Flow limiter
Serial no.
(type plate)
Flow rate
l/min
Colour
7544719 12 Red
7544720 14 Pink
7745530 16 Blue
7745531 12 Red
7544721 14 Pink
7544722 16 Blue
Checking the expansion vessel and system pressure
Note
The burner control unit can be removed to allow better
access to the test connector:
■
Pull the burner control unit to the right at the top until
the hook and loop fastening comes apart.
■
Undo the catch and remove the burner control unit
from the retainer by lifting it upwards.
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.
Commissioning, inspection, maintenance
Checking the flow limiter (only for gas condensing combi boiler)
5593201