Worcester 9.24 electronic boiler not heating water properly

Hiya hope you can help in some way
The problem with the boiler is that it doesn't heat the water up very hot. We have tried raising the temperature but still does not get hot. It also takes a long time to even get warm. An example would be running a bath or a shower, you don't need the cold tap on at all as it would run cold.
I would be grateful for any helpful advice you could give me.
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