Richard Butcher had put the visitors ahead just nine minutes when Richard Butcher volleyed home.
Scunthorpe came into the game, but struggled to create many chances before the break - with the left-back Marcus Williams seeing an effort go scooting over the crossbar and Ben May's going straight at the visiting keeper.
Things picked up for the home side after the break, with the midfielder Ian Morris going close with an effort that came back off the bar.
United finally levelled in the 90th minute when Hayes headed home from Morris' corner, and he completed the late turnaround when he turned the ball home following a goalmouth scramble.
Scunthorpe came into the game, but struggled to create many chances before the break - with the left-back Marcus Williams seeing an effort go scooting over the crossbar and Ben May's going straight at the visiting keeper.
Things picked up for the home side after the break, with the midfielder Ian Morris going close with an effort that came back off the bar.
United finally levelled in the 90th minute when Hayes headed home from Morris' corner, and he completed the late turnaround when he turned the ball home following a goalmouth scramble.