Columbia Gas is behind schedule in its ambitious restoration efforts in the Merrimack Valley, and was more than 500 homes behind in its plan to get houses up and running by Nov. 19, according to company data.

“The real challenge from the outset remains getting people’s houses and replacing people’s equipment. That remains a challenge,” said Andrew Maylor, town manager of North Andover. “Everybody involved and all the material available to residents and others shows that it’s not moving at a pace we’re comfortable with.”

In daily briefing materials published Monday, Columbia said 662 residential customers were “house-ready” as of Sunday, more than 500 less than the company’s plan of 1,196 customers.

House-ready residences in the Merrimack Valley have had their gas pipes and appliances replaced, and are ready to have gas service turned back on. Columbia has a total of 7,772 residential meters to turn on.

Maylor said the biggest issues have been a result of unexpected work needed to safely install new appliances and bring homes up to code.

“You get into someone’s house, you didn’t know what everyone’s house is going to look like,” Maylor said. “Everyone’s house presents a circumstance that’s somewhat different.”

Columbia has said gas service will be completely restored by Nov. 19. Until that happens, almost 7,000 in the Merrimack Valley have sought refuge in hotels and trailers.

“I’m concerned that the pace isn’t significant enough,” said Lawrence Mayor Daniel Rivera. “That pace puts the date in jeopardy.”

In a statement, Columbia Chief Recovery Officer Joe Albanese said resources had been focused on restoring service to some specific customers, and also said installation and replacement of appliances has been a challenge.

“Over the past several days due to the cold temperatures, we redeployed our workforce to focus on aiding the elderly and those with disabilities and health concerns,” Albanese said. “Additionally, some homes have required additional attention beyond the original scope to ensure these homes were safe for customers. There were various code issues, hazardous material issues, and other issues that have required our crews to spend several days longer than anticipated in some homes.”

Representatives for Columbia did not directly respond to questions about the company’s ability to make the Nov. 19 deadline.

While fewer houses are ready for gas than expected, Columbia is ahead of schedule with its pipeline replacement, the company said. Over the past three weeks, the company has outpaced its pipe replacement schedule and has now replaced 38.2 miles, 86 percent of the total. Columbia says it has more than 200 construction crews in the field.

— jordan.graham@bostonherald.com