vaillant combi TURBO max VUW 282/1 E do they have flow restrictor?

[Inverness]

I'm asking a question about the vaillant combi boiler as my mother in law is always complaining about the dhw only getting luke warm when tap is fully open and when showering it becomes intermittently luke warm to hot.

since it is a older combi I've looked at the instruction manual but nothing mentioned about a flow restrictor on the cold incoming supply.

I'm only in my 3rd year apprenticeship I've gathered on my on knowledge could be there isn't a flow restrictor on the incoming cold supply to the boiler? or the heat exchanger could be sludge up and becoming less efficient and blocked up with sludge particulars.