Problem with my Unvented water heater - OSO indirect 210

[Lyonser]

I'm new to all this so please excuse my ignorance on the subject. My water heater should work from both the oil condenser boiler which also runs the central heating and from the electric. The water heats fine from the oil boiler but wont work from the electric immersion. With the price of oil soaring and also good weather so i dont need heating i was hoping to have hot water by just switching on the immersion but had it on for over an hour and no hot water. There are 2 switches for the immersion and both red lights come on indicating there is power goin to them so i cant understand why it wont work.
Any help would be much appreciated.

 

[Onetap]

There are 2 switches for the immersion and both red lights come on indicating there is power goin to them so i cant understand why it wont work.

Maybe someone's taken a fuse out (I do, because the electric is usually much more expensive than mains gas and it is only there for emergencies) or the immersion heater itself is broken. The light indicates that there's power at the switch.

It's a 10 minute job for someone competent with a multi-meter to find out what's wrong.

 

[Lyonser]

There are 2 switches for the immersion and both red lights come on indicating there is power goin to them so i cant understand why it wont work.

Maybe someone's taken a fuse out (I do, because the electric is usually much more expensive than mains gas and it is only there for emergencies) or the immersion heater itself is broken. The light indicates that there's power at the switch.

It's a 10 minute job for someone competent with a multi-meter to find out what's wrong.

Thanks. Where would the fuse be - i think the installer mentioned something like that to me. There is a trip switch at the meter box labelled 'water heater' but it is turned on.