Luckily we can explore the data for somewhere like Newport. In the last 10 years it has averaged around 3.6 days per year where the temperature is 29°C or above, but 9 of those days happened in just one year!
Granted it is getting warmer and we are seeing it more but not exactly uncommon? Absolutely it is.
You're right, of course: my choice of words was poor.
29 degrees air temperature is uncommon (though getting less so) but is not extreme. However, the rail companies seem to treat cancellation of services as the default action rather than a last resort - today's services on the Ebbw Vale line were cancelled in the early hours, merely in anticipation of it being hot.
Hopefully, it's the old units that are failing, with the newer ones being removed from other services to replace them, although I imagine that TfW's new trains were ordered to the very cheapest specification and are probably not as resilient as they might be.

