Water heating can be a real hassle and not every home owner/tenant can tell what may be wrong by just looking at your water heater.

There is a rule of thumb that's very easy to remember. If there is water flowing but it's not hot then you most likely have an electrical issue (normally the element or thermostat) and If there is no water flowing at all or the water flow is severely less than normal then you most likely have a plumbing issue.

Gas water heats are the exception to this rule. You always want to call a plumber/Gasfitter first.

As far as the plumbing goes there is a wide verity of things that that could be the issue, from the water supply to any one of the valves. We will have to inspect your job to investigate further.

In the case of low pressure hot water cylinders there is no easy way to upgrade the pressure usually the best course of action is to replace the shower mixers with appropriate unequal shower mixers with a venturi or to upgrade the cylinder itself.