A unnamed person living in Aberhosan, Powys, was turning on their TV every day at 7am â€“ unaware that a signal from the set was interfering with the entire village's internet access.
Openreach engineers discovered the problem after first trying to fix the issue with a replacement cable.
The owner of the TV was "mortified" and agreed not to use the problem again, engineers said.
Workers walked round the village with a special monitor to try and locate any signals that could be contributing to the village's internet woes.
They soon found that one house was giving off a single high-level impulse noise (SHINE), that interferes with the proper functioning of other devices, engineer Michael Jones said.
"At 7am, like clockwork, it happened. Our device picked up a large burst of electrical interference in the village," he told the BBC.
"It turned out that at 7am every morning the occupant would switch on their old TV which would, in turn, knock out broadband for the entire village."
Openreach said that many electrical devices can have an impact on broadband.
Suzanne Rutherford, Openreach chief engineer's lead for Wales, said: "We'd just advise the public to make sure that their electric appliances are properly certified and meet current British standards.
"And if you have a fault, report it to your service provider in the first instance so that we can investigate."
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