I literally called my mate last night about this. Have not touched an unvented in ages. And now I have been to 4 in the last week. All Miles apart from each other. Whilst I have you all, went to this yesterday. There is a whole world of issues but not sure about this one? Vaillant unvented 260L cylinder on an EcoTec plus 837 combi and the expansion tank is piped straight into the inlet control valve. If I remember correctly this shouldn’t be like that, but a second opinion would be good.
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