Hot water cylinder puzzle

[Jimmyeatworld]

Hi all

I have a hot water cylinder that is heated both by a gas boiler and an electric immersion heater.

For the electric immersion heater, I have one heater but two adjacent switches. Please can someone explain? And should I keep one or both turned on?

A second puzzle is over the weekend, my boiler broke but I still had hot water upstairs (presume the electric heater was working) but no hot water downstairs. What is the reason for this given the hot water cylinder should supply the whole house?

 

[flameport]

And should I keep one or both turned on?

Normally the immersion heater should be off.
Much cheaper to heat the water using gas. The electric immersion heater is only there for situations such as when the gas boiler is broken.

The second switch could be for anything, or nothing. If everything works with it off, keep it off.

 

[Razor900]

You was probably just using up the hot water stored in the cylinder.

Are you sure you don't have a combi feeding the kitchen/downstairs outlets and an unvented doing upstairs?

 

[CountryFan]

Switches look linked, so could need both on or just one.

 

[Madrab]

+1 re if you have a combi boiler?

Looks like you only have one immersion element in the unvented cylinder or is there another one of these out of frame to the left?