A train company has apologised to passengers who were trapped on a sweltering train for four hours.
An investigation has begun into the breakdown
Virgin Trains said a full investigation into Tuesday's events was continuing.
Travellers on a Virgin service from Plymouth to Edinburgh found themselves stranded when it stopped at Tebay.
The 0713 BST train from Plymouth to Edinburgh should have arrived in Carlisle just before 1400 BST.
But passengers did not get to the city until after 1830 BST.
The train was already slowed because of speed restrictions imposed by Network Rail during the hot weather.
A spokeswoman for Virgin Trains said the company apologised to travellers.
He also said passengers were being offered a full refund and another free journey.
Nicola Jones, who was travelling from France to Carlisle, said: "We were left without any information for over an hour.
"These new trains did not have windows that could open so it was like a greenhouse effect.
"The air conditioning broke down and we were left with almost no air inside the carriages.
"We were eventually told that the brakes had failed.
"It was intolerable."
A Virgin spokeswoman said the service, which was made up of two trains linked together, suffered a "technical fault".
Overhead power cables and power on the rails were switched off while Virgin staff and the British Transport Police escorted passengers off the train, and along the West Coast Main Line.
Some passengers left the train and opted to continue their journey by road.
The Virgin spokeswoman added that a full investigation into the incident would be carried out.
The hot weather speed restrictions have brought big delays to other travellers on the busy West Coast route.
Many services at a slower than usual speed, amid concern tracks may buckle in temperatures of 30C plus.
Network Rail has imposed further speed limits on Wednesday.
The head of the Strategic Rail Authority, Richard Bowker, blamed Network Rail's predecessor Railtrack for some of the delays.