The alleged arson attack happened around 3am on Wednesday at a flat in Derby Street
The fire was confined to the rear of the property after a brown leather couch was set alight, which ripped through the bottom floor - including one of the rentable rooms.
The entrance to the flat smelt of smoke two days after the fire according to the tenants
Landlord Peter Rayworth said: "The fire crew told me the temperature was over 400 degrees.
"It melted two fire alarms, which are designed to withstand around 270 degrees. So you can imagine the heat - it would have been an inferno."