British Gas has paid a total of £1.1m to customers over missed appointments.
The energy supplier said around 12,000 mainly business customers were affected by third party agents who missed or were late for appointments and then did not compensate them as required by the regulator, Ofgem.
If suppliers and their agents do not meet Ofgem's standards on customer visits, they must pay compensation within 10 days.
British Gas came forward to Ofgem and said process errors had caused it to miss payments to some micro-business and domestic customers.
Britain's largest energy supplier paid customers the required £30 for the initial failed appointment and £30 for not paying within the required 10 days. In addition, British Gas paid an extra £30 to each affected customer for a total of £90 each.
A spokesperson for British Gas said:
We discovered the error last year and reported it to Ofgem. We have apologised to the affected customers, given them all compensation and an additional goodwill payment. In April this year we introduced new system checks to ensure this can’t happen again.
Martin Crouch, Ofgem senior partner for improving regulation, said:
British Gas did the right thing in coming forward to report this issue, and has since improved its processes to make sure that, when appointments are missed or not kept on time, all customers receive the compensation they’re entitled to.
It’s crucial that suppliers keep appointments on time, and make amends when things go wrong.