A Whangarei man hit with a $911 power bill two months after a Smart Meter was installed at his property is warning people to check their actual power usage themselves to avoid a similar fate.

Alan Graf and his partner are semi-retired, and had a smart meter installed at their Kamo home in March.

Smart meters are designed to electronically record more regular and accurate electricity use information.

But Mr Graf is wary of the new power technology.

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"My partner and I bought a new smartphone recently, and it's even smarter than us. These smart meters are just dumb," he said.

His first bill from Mercury Energy after the meter was installed was $630, which he got reduced to $254 after contacting Mercury.

The following bill was for $530, then this week he was slapped with a $911 bill.

He said he was aware of at least five other people, from Three Mile Bush to Regent, who had had similarly inflated bills, from various power companies.

"If I know of five people who have been affected, there's obviously a few people who this is happening to," Mr Graf said.

One was a pensioner who was hit with a $400 bill in a month when she was away from her home for two weeks.

He said he had now got his issue sorted with Mercury and was very happy with their response, but wanted to warn people to not just trust their energy bill on face value.

"The chappie I dealt with was great ... [But] he said unfortunately they can't do anything about it [higher bills] unless they hear from people."

Mr Graf said people who paid their electricity bills by direct debit may not even know they could be being overcharged, and he urged people to read their meters.

Mercury Energy said they had received no customer complaints about smart meters, and the meters went through a rigorous testing programme.

A spokesperson said that customers in a small number of cases who were coming off old meters, with a billing combination of physical and estimate readings, could notice a change in billing after the smart meter installation as it gave a more accurate reading, where previous bills could have under-reported the customer's usage.

About 10 per cent of its 11,000 customers on the Northpower network now had smart meters. The company expects to have most of its Northland customers on smart meters by the end of the year.