I have a Gainsborough power shower model 9.5 SCL and I'd like to know if I need a long (11cm) or short (8cm) PRD.
Also, which is the cheapest way to get one?
Gainsborough customer service should advise you on this.
If you quote the shower model /serial nr. they should be able to tell you the part nr. needed. They can probably sell you a spare. One question though, what made the PRD fail.
If it blew due at first commission, water hammer, etc.OK. If its an old unit check that the heater tank is not limescaled up