Central heating sudden failure

Hope someone can shed some light..... For no reason today, my hot water and heating failed. The boiler (Potterton Kingfisher) fires up, although the temperature of the flue gases are much higher than normal, and runs for about a minute before shutting down - possibly overheating. The pump is ok (have removed and checked & only 3 months old), and if i push the (2 port Honeywell) motorised valve round with a screwdriver, the pump starts, although there is a sound like water cavitation as if it can't circulate at all. The wiring seems ok, but I am not sure where to go next. I haven't got a lot of money at the moment, so it would be good if someone could guide me as to where to go next. A plumber is the absolute last resort!
Thanks
Russell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Before we go any further, bleed all of your radiators and any bleed valves you see elsewhere on the pipework, such as near the pump, boiler and zone valves.
The symptoms seem to indicate that no water is flowing. How are you sure the pump is working? Don't be distracted by the fact that the pump is new. The "bathtub" reliability curve indicates that brand new equipment is less reliable than stuff that has been installed and working for a couple of years.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

(i.e not a combi boiler or sealed system) If so the symptoms could mean that your header tank is empty and so there is not enough water in your system to allow the pump to drive it. This can happen when the ball valve sticks closed and the water slowly evapourates.
HTH Dave R
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.