>> Millions of households dont have the issue, its as likely as having a wasps nest block your overflow pipe
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How many overflow pipes were drilled slightly angled downwards to ensure water did not run back into the room? Icing up ?
It is easy to see condensate pipes from boilers also bodged.
In our first house when I removed "The Wonder Geyser" ( that appeared to have been unused for possibly decades )from the bathroom the whole flue through two 90 degree bends was stuffed with a starlings nest.
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