Some residents left without hot water until after 7am today.

Some Auckland residents were without hot water until late this morning following yet another fault with Vector's electricity network.

A total of 85,000 Vector customers lost power after a fire at a Penrose substation on Sunday.

Vector spokeswoman Sandy Hodge said some Remuera and St Heliers residents remained without hot water until late this morning after a signal failure sent at 1am failed to restore power to affected residents' hot water.

The signal was successfully re-sent at 7am, she said.

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Watch: Power outage - Aucklanders wake to no power

Tens of thousands of Aucklanders could remain without power for up to two days after two fires damaged Transpower's Penrose substation early today.

"People when they're on a controlled rate - which means they're on a cheaper electricity rate because they opt into it - can can have their hot water controlled.

"Only those people with their hot water controlled are affected and only some of those in pockets of suburbs."

Ms Hodge said she was unaware of the exact number of customers affected.

"If people give it an hour or so and run their hot water tap and it's lukewarm or it's heating up, then it's been fixed."

Hot water 'load management' was undertaken on Vector's network in Auckland yesterday as power was slowly restored to suburbs affected by the power outage - cutting hot water to customers on controlled rates, Ms Hodge said.

"Those people on the controlled rate - we sent a signal to their hot water cylinders to turn it off so we could keep the load low.

"We switched that back on at 1am this morning so that the load could pick up when the other normal day-to-day heaters and stuff was not running."

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Read more: Auckland blackout: Shock to the system - Why did it happen?

Ms Hodge said it was "very unfortunate" that some affected residents had paid tradespeople to check their hot water cylinder only to be told that there was nothing wrong with it.

However, the company had yet to confirm whether compensation would be offered.

"The people who weren't on the controlled system wouldn't have been affected."