began service on the Heart of Wessex Line, as well as operating some services on the Wessex Main Line as far as Warminster and Southampton Central. In January 2019, they also began operating the regional service between Cardiff Central and Portsmouth Harbour which allowed more of the Class 158 units that solely operated this service to move more west. In December 2020, they began operating on the Riviera Line and Avocet Line following the retirement of the Class 143 units. The transfer of the 166 (and 165) units to services in and around Bristol and Exeter have overall allowed units that previously operated these services to move further west, such as the Class 150 and Class 158 units. While the majority of the fleet is based at St Phillip's Marsh depot now, some of the units still do remain based at Reading TMD for Thames Valley services where they were all planned to be replaced by Class 769 units. London and Thames Valley Refresh Towards the end of January 2010, First Great Western announced an £8 million refresh programme to their fleet of Class 166 Turbo DMU trains. The carpets and seats were retrimmed, interiors repainted, Passenger Information Displays replaced with a GPS-based system, and toilets upgraded. The refresh work was carried out at Reading Depot. All 151 vehicles have now been refurbished. In late 2014, another set of refreshes to the Class 166 was started. The changes made during the 2010 refresh remain in place, with some upgrades, including the fitting of LED head/tail lights, new toilets which are more accessible than the old toilets, new door buzzers & new door buttons of the standard design with a round button on a yellow ring. All units have now received the refresh. Unit 166204 was named in honour of Twyford station master Norman Topsom MBE who retired in November 2015. Fleet details Liveries and interiors References 166 Train-related introductions in 1992 ABB multiple units