Good news!  You do not need to fit an isolation switch to existing Hot water units, even if you replace the unit like for like.

ONLY new wiring installation from OCTOBER 2017 require a new isolation switch to be fitted from day one.

All new electric Hot Water units require an isolation switch to be located near the Hot Water unit.

This rule is not retrospective and is not for existing installations; the new rule applies to new full installations or any relocations where a new circuit is to be installed,  new wiring installations; new houses, etc.

In summary –

• New installations or if the wiring is replaced- The hot water unit requires an isolation switch.
• Plumbers with a restricted electrical licence, who replace the Hot Water unit, like for like
• No isolation switch is required if existing & the there is no alterations to the cabling.

Should the wiring be required to be altered, the Restricted electrical person must engage a full electrician to completes this work.

Basically, there are minimal changes to the existing.