Spark faces a bill of more than $1 million as it asks fixed wireless home phone customers to return their power back-up hardware. The company went public with the recall on Saturday. More than 14,000 customers are affected.

The recall comes after a customer reported their unit had overheated with smoke emerging from the device.

After investigating the fault, Spark said it found “wiring inconsistencies” in a handful of devices that it tested. The company recalled the products because they are a potential fire risk.

The power back-up hardware is part of a kit that was sent unsolicited to customers Spark wanted to move off the copper network and on to its wireless service. Spark targeted customers who previously only had a voice landline service without broadband. These are mainly older people.

In some cases these customers were told by Spark service agents that copper network was closing and they needed to move onto wireless. This is not the case. The Commerce Commission investigated the practice but decided not to prosecute.

Customers were also sent suitable handsets. While these will work without the back-up power supply, the units were only to cover customers during power cuts, some will now be returning to the copper network.