Hi - my water got cut off yesterday whilst I was having a shower. The water came back on later but I have no hot water - I think the tank probably emptied when I was showering but maybe didn't fill back up. Is this likely to be the problem or maybe there's an air-lock? Whichever can anybody give me some steps to rectify as I'm sure its probably a simple solution!

If your tank was empty and the element was turned on your element has burned out and will need to be replaced. There is no easy fix for this problem other than replace the element.

What if it was a gas hot water heater? (no element)

Go to the water heater and attach a garden hose to the drain spout. Empty some water from the heater and feel the cold water pipe at the top of the heater. You should feel the pipe getting cold because fresh water is being replenished as you drain the tank. If fresh water is going in, after turning off drain, now turn on a hot water tap and feel if the hot water pipe at the top of the water heater is hot to the touch. If you do not get hot water but you get flow out of the tank, if it is a gas water heater, check to make sure the pilot is on. If electric, after turning power to the water heater at the breaker, remove the top and bottom inspection ports and press in a small red reset button. Replace the panels and turn the power back on. In an hour or two, turn on your hot water tap and check for warm water. If still no hot water, you will need to get a technician involved.