The power cars were fitted with Voith cooling systems in 2003 and Voith carried out a major overhaul of all 134 cooling systems in 2011. A second major overhaul is now due and this work will be carried out at the Voith Turbo Service Centre in Greenford near London.

All components will be cleaned and inspected using non-destructive testing techniques, and the programme will include renewal of standard wearing parts.
The HSTs operated by GWR originally entered service between 1976 and 1982 and the 200km/h trains are due to be replaced by new Hitachi class 800 and class 801 trains from 2017.