Sudden hot water pressure problems

[SausagePies]

Waking up this morning we have discovered that there is very little water pressure in the hot taps upstairs, and the shower does not work at all.

The cold water taps everywhere are fine.

The hot water taps downstairs are running a bit slower than usual, but I'm not sure if I'm imagining that, or if they have always been like that.

The hot water that is running seems to be really really hot.

Any ideas what could be wrong?

What type of a boiler do you have? A hot water tank or hot water on demand from a combi boiler?

It is a Worcester HeatSlave 15/19, oil powered, combi boiler.

If you are absolutely sure that the pressure and flow at the cold taps is unaffected (fill a bucket, time it, calculate litres per minute, compare it to hot taps) then perhaps you have a blockage in the boiler's heat exchanger. Might be limescale. Ask whoever usually services the boiler to have a look.