Viessmann Vitotwin 300-W Installation And Service Instructions For Contractors page 46

Installation sequence
Gas connection
!
Please note
Excessive test pressure may
damage the boiler and the gas
valve.
Max. test pressure 150 mbar.
Where higher pressure is
required for tightness tests,
disconnect the boiler and the
gas valves from the gas sup-
ply pipe (undo the fitting).
46
(cont.)
3. Vent the gas line.