Recently had plumber & builder to remove back boiler & seal up chimney breast along with room air vent. Replaced with a condensor boiler in the loft. The chimney was sealed with breeze blocks & plastered. Since having heavy rain/strong winds condensation has formed on the inside wall where the room air vent was. Builder put a brick into the vent space & plastered over & didn't remove external vent, what do you recommend?
Should we seal chimney top, now have concerns about rain or bird debris, however we never had any damp or bird debris when the back boiler was in working?
Appreciate any thoughts or recommendations.