Two companies charged over a fatal gas explosion in Onehunga will face a hearing next year.

Watercare maintenance planner and mother of two Philomen Gulland, 48, was killed in the explosion on June 4 last year. Three others were seriously injured including engineer Ian Winson, who lost part of both his legs.

Watercare and contractor Canadian Pacific Ltd pleaded not guilty to charges of failing to ensure the safety of their employees and a defended hearing has been scheduled for next September.

Watercare faces three charges under the Health and Safety in Employment Act, and Canadian Pacific Ltd, two charges.