The options as I see it are 1) Contact a Triton agent and find out if a spare solenoid valve is available - and how long it would take to get one 2) Replace the shower with exactly the same model (saves pipework alterations 3) Put an isolator valve in the shower mains water feed so it can be isolated and repaired at your leisure. I'd go for 3 for a start - any shower maintenance means that it needs to be isolated anyway.
John
June 2008