The fill pressure of combies is 1.2bar, when he drained down and then re pressure the expansion vessel to 0.75bar the flushed via the filling loop.
Then then new part can be fitted + Air vent and fill with 'boiler silencer like X200, re pressure to 1.2 bar and vent boiler as ness.
Your W240 has a 8ltr. vessel, may be too small for the system and may need external fitting to the return. This is advanced work!! NOT for DIY.
Mr Combi
March 2009
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