how do i fix my pulsacoil 2000?

the boiler is only delivering luke warm water to the taps how can i fix this problem ?
have replaced both emmersion heaters.
changed the wiring from off peak to on peak as only 1 person in the flat.
replaced broken ball valve as tank was not filling.
boiler code flashing operating correctly.
The control panel switched to constant all day and night but still only luke warm water.