Auckland Transport's not impressed by heat causing train cancellations.

Some services were canned on the Eastern, Western and Southern line today, after track steel reached 48 degrees in parts.

AT's Stacey van der Putten says people deserve better than a network that can't run at capacity on a mildly warm summer day.

"What we're seeing over recent weeks is what I'd call a reliability failure- that's been pretty consistent. Of course it's when everybody's coming back to work, coming back to school, it does have a huge impact on trust and confidence in our network."

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