A nine-mile diversion will be in place near Stowmarket for several weeks while Anglian Water carries out works.
Engineers are repairing a collapsed sewer in Saxham Street, between Stowupland and Mendlesham. The road is not believed to be scheduled to reopen until April 10.
The work comes following problems in the area in December, but was brought forward from when it was originally planned after the sewer collapsed.
A spokeswoman for Anglian Water said: "Our teams are currently repairing a collapsed sewer on Saxham Street in Stowupland.
"While we fix the sewer, we are using tankers to keep toilets flushing and sinks draining for customers in the area.
“In order to keep our teams and other road users safe while they work, we have worked with Suffolk County Council and Highways to put a full diversion in place.
"Saxham Street will remain closed for the duration of the works, with two-way lights on the A1120 and one-way traffic on Blacksmith’s Lane. We’d like to thank everyone for their patience while we carry out this emergency work.”
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