Worcester CDi 40 conventional overheating

[horhay]

I fitted this boiler today.Stripped out a conventional boiler and fitted a new one. I fired up the heating and everything was fine, radiators were heating, hot water was heated, zone valves and pump worked great. It ran like this for about 2 hours. When i put the heating off i noticed the pump had an over run. I turned off the heating drained the system and cut in a bypass, when i filled the system and put the heating back on the boiler went straight up to over 90 degrees and the the display read U1... U2... U3. At this point i put the boiler off let it cool down and tried again and again but the boiler keeps on over heating. The zone valves are working and i can here the pump is still running. Any ideas guys, has any one seen this boiler do this before

 

[dal5band]

May be an obstruction in the circulation - separate bits of debris show no signs but when they wedge up against a valve or pump inlet, it becomes a blockage. Had this with a hot water pipe - bit stuck in the tap.
Just a thought

 

[horhay]

I have flushed the system cold then hot then with sentinel. So its been well flushed. Could debris still be in the system