Sprinklers failed to come on automatically when crude oil caught fire on CNR International's Tiffany platform in January.
It is understood the water sprinklers had to be triggered manually to stop a disaster.
Yesterday the Health and Safety Executive (HSE) confirmed another fire broke out on the platform last weekend.
Production has now been halted on the rig and it is at the centre of a major safety probe as union chiefs call for operators to up their game on maintenance procedures. An HSE spokeswoman said: "CNR informed HSE of a fire incident on the Tiffany platform on Sunday, April 6, and HSE has sent investigators to the platform.
"HSE can also confirm two improvement notices were served in relation to a separate incident in January, but as one notice is still subject to an appeal period, no conclusions can be drawn as yet and we will not be making any comment."
The North Sea oil and gas industry is currently gearing up for a summer of planned safety maintenance programmes that were put off last year.
A spokesman for CNR International said a small localised fire had broken out on the production deck of the rig last Sunday at around 11am.
He said the fire was extinguished by the platform's fixed systems and emergency response team.