Is it my water heater that's bust or something else?

[gwilson]

Hi

Hoping someone can offer some advice as I'm pulling my hair out!

I live in a very old small tenement flat. Hot water is provided by a single "Stiebel Eltron" water heater - basically like a giant Electric Shower that feeds the hot taps & shower itself (as far as I can tell).

Problem is this - seems to me that the performance of the water heater is a bit sporadic. It can be hot one minute and then a couple of hours later it can be pretty cool. Trouble for me is that lately, it's been FREEZING first thing in the morning when I need to wash/ shower for work!!

I'm not a plumber so I don't know if it's the heater itself that needs to be replaced or if there are environmental factors that could affect it's ability to heat the water.

I would have thought that if the mains cold water was too cold the heater would output more slowly (i.e. less flow to the shower/ tap) but this is not the case. The pressure from taps/ shower seems to be the same, it's usually the temperature that's varied.

Any advice?

Thanks very much

Gordon