Andrew Link, who has been diagnosed with paranoid schizophrenia in the past, had been smoking cannabis before he attacked the man and accused him of sexually assaulting his girlfriend, an allegation that was unfounded.
Link, 45, was staying at accommodation for the homeless on Castle View in Pontefract, while the victim was in another bedroom on the same floor, prosecutor Caroline Abraham told Leeds Crown Court.
The victim later said that Link would often shout at him and threaten him.
On May 30 last year, the victim went to pub in Pontefract for the afternoon and came home when it got dark.
He went straight to bed but was woken a short time later by the sound of his bedroom door opening and noticed link stood over him with the kettle. He then poured the boiling water over his chest.
The neighbours, who said they had been threatened by Link in the past, were alerted by the screaming and went to the address to knock on the door. Link opened the door and the victim then ran out.
The police arrested Link who told them he did it because his girlfriend had been raped by the victim and he "wasn't getting away with it".
During interview he gave no comments, but at one point said: "I know it's bad".
The victim was treated in hospital and despite burns to his chest, was told he would have no permanent scarring.
Link, who has been held on remand at HMP Leeds since June last year, admitted GBH with intent.
The court was told Link had lengthy criminal record which included burglary, affray, handling stolen goods and wounding, for which he received a 21-month sentence in 2001.
Mitigating for Link, Satpal Roth-Sharma said he had been prescribed medication for his schizophrenia, but had stopped taking it in the days up the violent attack.
She also said he had been smoking cannabis so there was "an element of paranoia".
Mrs Roth-Sharma said there was no evidence that there had been a sexual assault on his girlfriend, who herself denied the claims.
Mrs Roth-Sharma said: "He accepts full responsibility and there was a degree of planning."
She added that he was physically abused a child and was burnt and beaten, and had turned to heroin.
Judge Mushtaq Khokhar jailed Link for three years and said: "It's a worrying case.
"You have admitted that you hear voices and have visible and audible hallucinations.
"You formed the view that the complainant sexually assaulted your girlfriend, of course that was not the case. It was a figment of your imagination.
"You say you are remorseful but you are not.
"Unless you change your ways you are going to find yourself in the same situation."