Slow running mixer tap to bath but sink runs fine?

[gcltd]

Hi, our bath mixer runs slow, worse on the hot tap, the sink which is on the same pipes just before the bath also has a mixer and they both run fine?
The O rings are fine as new ish taps.

Also hints or advise please?

 

[Armo74]

Check isolation valves are fully open,Could be partially blocked. A bit more info on the type of system would be useful.

 

[JohnD]

How many litres per minute do you get from the hot bath tap, and from the hot sink tap?

Is it a stylish new bath tap?

Do you have a combi boiler, or a water tank in the loft and a HW cylinder?