We have very low ( down to a trickle) pressure on all out hot water taps. The pressure is good on the cold. Can anyone advise what the problem is. It never use to be like this :( would be nice to have proper hot running water :)

Try the drain at the bottom of the tank, normal pressure/volume?

How old is the waterheater?

If your water heater has "heat trap nppples (see image) that will block The flow. If the nipples in the inlet and outlet of the heater are brass you're OK but I'd replace anything else. Good luck, Tom