ferroli optima dhw is lukewarm?

Hi I have a Ferroli Optima (not sure of the model as this was here when i moved in). Recentley I have noticed that when i run the hot water taps, the water is now no longer hot, just lukewarm.

When i turn the tap the pilot light ignites and remains on for the duration the tap is running, however the water does not get any hotter. The CH works fine without any problems.

From looking at the curcuit board it resembles that of a Optima 901. Any pointers would be greatley appreciated.