Stanza 8.5 kW electric showers are the most suitable retro-fit replacement models:
Stanza 8.5 white*
Alternatively, the following models could also be fitted but may requires some alterations to the pipework and wiring:
8.5 se - with a gloss white finish
8.5 cse - with a satin chrome finish
8.5 gse - with a stylish graphite finish