Water Heater Timer Replacement Safety

[rcreff]

Hi my water heater timer has ceased to work correctly (still works when turning it manually) so I have bought a replacement. I was wondering, there is a red switch between the water heater and timer unit when I turn it off the timer turns off.

Is it safe to replace the timer with just this switched off or do I have to turn the mains off, I would usually just turn the mains off to be safe but I can only replace the unit in the evening. I would prefer if I could just take my time and replace it while the rest of the family carry on normally. Plus I would be able see what I am doing.

 

[luminaire]

It is always best to play safe with electricity therefore you need to switch off at the mains.
The red switch is there to switch off the supply to the water heater. Even so if you were to be working on the water heater you would still switch off at the mains, and make sure no one can come along and switch it on whilst you're working .