Belling Malaga mk1 1997 flue question.

[npjrogers]

We have a Mk1 Belling (now Propex) gas water heater in our van. All the more recent Propex models have two separate air flue vents, (exhaust is the larger round one and air inlet at the bottom with an elongated vent.) My mk 1 appears to only have a single vent with the air entering through an annular gap around the exhaust vent. This is sometimes known as a balanced flue. My fluebox has at sometime suffered from external rust and a repair patch has been applied below the exhaust. I am worried that this will disturb the air flow and could be dangerous. Did the Mk 1 Belling have a two vent system and if so did the repair blank off the air inlet hole?