This report deals with the operating experience of the high temperature valves on the fluidized-bed ash removal system and the primary cyclone sampling system. The main operational problems of valve leakage and sticking are discussed and details are provided of the measures being taken to alleviate the difficulties. At the termination of Test Series One, all the valves were stripped down and inspected. The modifications, which are being undertaken as a result of the inspection are outlined, and these include the installation of thermocouples, nitrogen purging facilities, and alterations to the seat arrangement and the trunnion bearings. The development of cracks in two of the valve bodies and seats has caused concern. Expert advice has been taken and it is considered that weld repairs of the cracks could produce further cracking and possible distortion during post-weld heat treatment. Therefore, repair of the cracks has not been attempted. Procedures for regularly monitoring crack growth are to be established in preparation for Test Series Two. Operating the valves at the required temperature and pressure has proved reasonably successful, and it is considered that the problems that have occurred can be rectified.