Resident William Rennie, 78, who has lived on his own since his wife died six years ago, put the heater on to warm up water for his bath at about 10am on Sunday.
Half an hour later he discovered smoke on the landing of his home in Moorcroft.
"I never thought this house would set on fire," he told the Knutsford Guardian yesterday. "Just shows how wrong you can be."
The immersion heater was in an airing cupboard in the bedroom which also housed the plastic water tank which melted in the fire.
By the time Knutsford Fire Brigade got to the scene the flames were out thanks to the water in the tank.
Most of the bedding and towels kept in the cupboard were destroyed in the blaze although some only suffered water damage.
Yesterday Mr Rennie was continuing his bid to clean the first floor of his home which had a lot of smoke damage.
"It's just a case of cleaning the walls now but I've run out of Flash," he said.
The cupboard was completely destroyed by the blaze but a spokesmen for the fire brigade said that the consequences could have been much worse.
"It was lucky that the tank was plastic and not metal because it would not have melted otherwise," said the spokesman. "There was no smoke detector in the house so the results could have been disastrous."
Mr Rennie agrees that luck was on his side.
"I'm just glad that I wasn't asleep or else who knows what could have happened," he said.
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