The hot water at your kitchen sink will always be hotter than the water in your bathroom.
The water at your kitchen sink is set to 55 degrees, whereas the water in your bathroom will be around 40-45 degrees. This is by design.
The reason why the water in your bathroom is a lower temperature than at your kitchen sink, is because the Building Regulations require Developers to install a thermostat mixing valve (or TMV) under your bath. The TMV mixes the hot water we supply with cold water to produce water at a safe and comfortable temperature for washing and bathing.
The water at your kitchen sink needs to be hotter to kill bacteria when washing up your dishes.