A power company is offering the chance to pay all household costs in one bill - but consumer groups warn the convenience may come at a cost.

Trustpower, which offers energy and telecommunications services, says its plan will make it easier for customers to pay everything - phone, electricity, gas and internet - in a single bill.

But experts warn that consumers should beware of what that convenience might cost them later.

Consumer NZ chief executive Sue Chetwin said the idea was a good one, as people were always looking for more convenient ways to get things done.


But it would be up to customers to make sure they were getting their money's worth.

"What they'll be selling to customers is that it's easier," she said. "But make sure the savings are there and that you're not just paying for convenience."

Ms Chetwin said Trustpower was one of the more expensive electricity providers in the country, but might have cheaper broadband or phone rates, making it a better bet for customers.

Energy expert Molly Melhuish said the service could lead to customers getting stuck - making it harder to for them to leave the company.

"It makes you a sticky customer ... so if you do join up, look from time to time at the gas portion of the bill, for example. Make sure you compare all the time and that there aren't any penalty clauses.

"It's good in principle, but be careful in practice."

Trustpower, based in Tauranga, has been in business for almost a century and has traditionally sold electricity.

Its gas service - reticulated gas and LPG - started last year and phone and broadband services have been available for eight years.

The all-in-one bill is being promoted to residents and businesses in Auckland and Hamilton from this week, and will later be offered in Wellington.

Trustpower spokeswoman Carolyn Schofield said the move was the result of customer demand.

"What we were hearing from our customers was that they wanted something where they would be able to bundle all their bills into one.

"It's more convenient and it means that there's only one company to deal with."

Budgeting expert Darryl Evans, who is head of the Mangere Budgeting Services Trust, said the only downside to having one bill was that struggling families could be left in the dark - literally.

"Having all the bills together would be quite a large bill and that can be frightening. If you can't pay it all off, then everything would turn off."