A seller is not obliged to volunteer information about issues with the plumbing to a buyer.  There are some questions in standard property information forms which ask about things such as whether or not the boiler is in working order and whether or not the property or surrounding area has ever flooded.  If there is evidence that the plumbing issue in question existed during the period of the seller’s ownership, and the seller has actively mislead the buyer by suggesting that such an issue did not exist (which is not the same as staying silent on the point), then there could be a misrepresentation claim.