Combi-Boiler problem

[linc1464]

Hi Folks,

I have a Halsted combi-boiler. For about the last three months, turning on the hot tap has failed to turn it on to provide hot water. However, it works perfectly for the central heating and comes on exactly when supposed to using the timer.

I'm pretty useless at this sort of stuff so will probably call out an engineer. However, I was looking to understant what it might be first (to try and avoid being conned!). Some quick internet searches leads me to think that it's some sort of pressure loss problem. Does this sound about right, what could cause it and is it likely to be expensive?

Thanks in advance
Steve

 

[linc1464]

I just want to add some stuff to my previous post, sorry. The cold pressure of the boiler is approx 0.4 bar (it doesn't drop below this) and this rises to 0.7-1 when on. All radiators are red hot and don't seem to have leaks.

I just want to mention that a few weeks ago, i replaced some tap washers and turned the stop tap off. I guess i didn't turn it back on fully (maybe one turn). Could this be the problem (i don't really want to mess with it unless it could work)?