Worcester 25Si ...Hot water not firing up at low pressure?

I've got a Worcester 25si around 7 years old combi, recently it decided to have a problem with the hot water.

You will need to turn the tap at full power in order for the hot water flow switch to kick in. At full tap open, you can hear the microswitch clicking and the red indicator for the hot water illuminating. When you turn the tap at half way the switch doesn't engage. I have looked at the micro switch mounted on top of the hot water flow switch and works fine as well as it is in the right position.

The water pressure i get to the taps is also fine.

The water pressure from mains to the boiler is fine, and the heating to the radiators is fine too.

The boiler is powering my shower and it is very annoying that the hot water is not working properly. It has been working fine for the last 6 years.

The hot water flow switch has a red valve on it that if you turn it different directions it regulates the water pressure to the boiler. Now when I play with it I don't see any change in the water pressure at the taps. Does it only regulate the pressure to the boiler and not to the taps ?

What do you think it's wrong ?. I'm suspecting the water flow switch filter is clogged and need cleaning, possible ?

Please advice....



This is the manual:

http://www.worcester-bosch.co.uk/index.php?fuseaction=site.viewFile&id=255810