Viewers of Arte, which broadcasts highbrow programmes to France and Germany, could not watch their favourite channel on TV from 7.00am Saturday till 12.26, although it was available on the the channel's website.
The heat at its headquarters in Alsace, eastern France, was so intense that an electrical supply unit caught fire.
The flames also seem to have knocked out the emergency generators that should have provided back-up.
At 39°C, Strasbourg was one of the hottest places in France Saturday.
Although 13 fewer areas were on orange alert, Lyon and much of eastern France were sweltering under temperatures around 37°C.
The heat was intense on the main motorway heading south from the capital, which was packed with the first major exodus of holidaymakers of the summer.
There were a total of 300 kilometres of traffic jams across the country on Saturday, in some cases doubling journey times of families hoping to reach the Mediterranean beaches.
Rail services were not affected, according to the rail company SNCF, although the heat did cause delays earlier in the week.
The authorities said Saturday that it was too early to say whether there has been a significant rise in physical casualties.
Doctor Patrick Pelloux, who sounded the alarm in the 2003 heatwave that cost 19,000 lives, said there had been a 20 per cent rise in calls to emergency services in heatwave-affected areas on Friday night, although he added that lessons have been learned in the last 12 years.