Celtic FF combi boiler

I have got problems with getting hot water from the boiler, the central heating when switched on works perfectly but when I turn the hot water tap on either in the bathroom or in the kitchen the boiler switches off (no central heating) and I get no hot water, if I switch the central heating off and try the hot tap again I still do not get any hot water, any ideas???
please help!

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.