Combi boiler....water hot...then water cold...

[MsFunshine]

Ive inherited a Worcester combi boiler in the house I've bought....and seem to have a problem with the hot(or not..) water. When I turn it on in either the kitchen or bathroom its obviously cold for a while...then becomes lovely and hot... but then after a short while it runs cold again
I've tried turning the tap 'down'....turning it 'up' but cant fathom the problem.Getting a bath full of hot water is impossible...
So the new bath I'm just fitting seems a bit of a waste of time *sigh*
Any suggestions greatly appreciated please...
MsF

 

[DarkInferno]

crud in the dhw (water to water) heat exchanger.

give it a few taps whilst running water through it should dislodge anything stuck in there

 

[ChrisR]

A tad optimistic perhaps, DI!?
Which boiler/how old.
Probably IS sludge/scale probably in the secondary (tap water) heat exchanger - but they haven't all got one!

 

[DarkInferno]

Ya I know... but as MsF didn't give a model number I just gave a generic answer to the boiler of my choice.