The road had been closed off since May with residents complaining of no or little work progress.
A spokesman from Herts County Council said: “Work started on Monday (September 18) to fill the main void up to a level just below the Thames Water sewer so that they can take over the site and repair the sewer.
“Once this work is complete, our contractor Ringway will continue to fill the hole with concrete to just below road level.
“Other utilities companies will then inspect their services to make sure they are safe.
“Once complete, the road surface will be reinstated and the road reopened.
“At this stage we estimate that this will happen at the end of November.”
Councillor Graham Adshead said that the biggest impact for residents has been the diversion of bus routes.