As record temperatures hit much of the UK on Tuesday, tech giants Google and Oracle suffered outages due to cooling systems failing at London data centres.
Data centers are large, highly secure buildings that house banks of computers and are the driving force behind many online services.
However, concentrated computing power generates heat so strong that cooling is necessary.
Both companies say the issues are now resolved.
Oracle, a major US database software and technology company, reported overheating issues just before 4pm BST.
“Following unusually high temperatures in the southern UK (London) region, two cooling units in the data center failed when they were required to operate beyond their design limits,” the company wrote in a status page first seen by The Register.
“As a result, temperatures in the data center began to rise, causing some systems to shut down as a protective measure.”
The company said the problem had been fixed in an update published shortly after 10am BST on Wednesday.
As Britain baked, overheating also hit the Google Cloud data center location in London.
Google Cloud allows other companies to work on company computers.
Just after 18:00 BST, the company announced that “a cooling failure has occurred in one of our buildings”.
To prevent damage to the machines and a longer outage, the company said it had shut down some of them.
The problem was fixed at 7am BST on Wednesday and the company said it only affected a “small group of our customers”.
Because the data being processed can be very valuable to their customers, data centers are built with many backups, including large amounts of cooling capacity.
Experts the BBC spoke to on Monday doubted that modern data centers would struggle, so failures by big, well-resourced companies like Google will come as a surprise.
But operators were wary of unprecedented temperatures.
Paul Hone of Redcentric, which runs data centers in Harrogate, London, Reading and Cambridge, told the BBC the firm had put its disaster recovery plan into action on Monday.
Mr Hone added that while data centers are designed to withstand hot weather, the heat temperatures would be at the “high end of design expectations for many data center operators”.
In the end, Tuesday passed without incident for Mr. Hone.
However, additional cooling means additional electricity consumption, which in turn can mean increased carbon emissions.
As climate scientists warn that very hot days will become more frequent, technology firms are exploring greener cooling solutions and computer systems that use less energy and generate less heat.
Microsoft conducted an experiment with an underwater data center off Orkney in 2020. Part of the attraction was the natural cooling provided by the surrounding seawater.