Boiler losing pressure

I have a C&M Britony 80 combi.
Every day I pressurise (fill) the system, and within a few hours the pressure drops back to 0, with water dripping out of the overflow on the back on the boiler?
Any ideas what the prob is? Somesort of overpressue valve? Expansion vessel inflation etc?
Any idea appreciated.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.