alpha combi boiler 240x hotwater problem

[dreamstorm]

i had my boiler checked it is running at 97% using an emmissions test, corgi plumber could not find a problem, heating works great comes on straight away hot water however does not kick in unless i run a bath and then its luke warm but if i turn on the sink tap before i turn off the bath then the hot tap will be hot, any help would be great

Paul

just an add on i have found the problem its the manifold (sanitary section) tap h2o gone comleatley, looks like where pin comes out to switch on heating for tap water is locked, drip marks on the lower plate and limescale all around the copper pin, i was wondering do i need to replace the manifold or could i strip it and clean out the lime scale after which, which would be a good seale? can i use gasket seal or i was thinking if you would know if there was anyother type of seal i could buy?

any help would be great..