our worcester bosch 240 has had a new diverter valve fitted by a brit gas engineer. Following the fit the pressure went from a constant 0.7, up to 1.5. Following the fit the heating didnt work but the hot water did. He returned and fitted a new pump and auto air relief. Heating still didnt work. Returned today, replaced diverter valve, the pressure rockets up to 4! He says the expansion vessel needs replacing. I'm not satisfied with the buys integrity (replacing unneeded parts, instaling fualty parts. Could it be that the pressure issue is a result of the work he has carried out? The pressure only became an issue after his first of 3 visits?
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.
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