Officers believe Drew Morris, 26, may have information about the raid at the victims' home in London Road, Halstead, on 26 April.
The man and woman, aged in their 60s, suffered severe scalding during the burglary.
Two men have been charged in connection with the incident.
Kacey Adams, 33, of Covert Road, Hainault, Ilford and Daniel Wallace, 32 and of no fixed address, are both charged with two counts of grievous bodily harm, two counts of false imprisonment and aggravated burglary.
Both men are currently remanded into custody, pending future court dates, Kent Police said.
A 29-year-old man remains on bail until 15 September.
Anyone with any information about Mr Morris is asked not to approach him but to contact Kent Police by calling 999 or 101.
Police investigating a burglary in which a couple were beaten and doused in boiling water have released details of a man they want to speak to.