The Firefighters Union says a recent life-threatening equipment failure at Thursday's massive North Shore Recycling Plant blaze wasn't the first.

Two firefighters needed rescue when their aerial unit broke down above the dangerous Wairau Valley blaze.

Vice president Martin Campbell says this again highlights that the fleet is ageing and poorly-maintained.

"In the days leading up to it, there were several faults with it - but unfortunately, we just don't have the trucks out there to replace it with and they don't have the time and money to make sure it's working properly."

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