Do electric boilers run out of hot water?

I moved into a new rented property about 3 weeks ago in the UK. I put on the heat, which is water-filled radiators supplied by an Electric Boiler, a Range Senator 6W, and a medium-sized water cylinder. I have never had this type of system only ever a gas/electric mix so I wasn't really sure how long it should take for the radiators to heat up!

It took about an hour and a half to get to kinda hot, like lukewarm. Is this right? The same with any hot water? and the tepid water only seems to last about 4 hours, shouldn't a boiler produce warm water into the pipers relatively quickly? and keep in the tank for a while?

I'm having no luck with landlord. They have sent out an electrician who didn't know anything about electrical heating systems. He said he thinks something it wrong as when its turned on the pipes leading from the boiler didn't warm up at all after 10 mins of being on and told me just to turn it off until it could be looked at. I am now waiting for a plumber, so who knows how long that could take?

To top it all off, I checked how much my electrical bill was for the first 2 weeks I was in the property. It was over £70! This cannot be right I'm not even warm and was putting it on for less than 1.5 hours a day. Is this normal for this type of system?