Banging Boiler Shutting Down

[niamhinho]

I have a Glowworm 100FF gas boiler. On saturday, I drained the whole system and replaced an old radiator. It then took me ages to refil the system. After bleeding all the rads, they are now full. I also opened a vent I found near the hot water tank which expelled plenty of air.

When I restart the boiler, it fires up and starts to heat the water. After about 2 minutes, there is a lot of banging, and it shuts down, although the overheat switch does not trip.

I have checked the F&E tank, which is full and the ballcock is OK. The pump seems fine (it's vibrating and I've bled it) and I've switched the zone valve to manual just in case. Could it be a partially blocked cold feed?

Thanks in advance

 

[ChrisR]

Partially blocked would still pass water
It'll be air still stuck, or sludge or pump, causing poor water flow.

 

[niamhinho]

It would still pass water, and has given that the rads have filled up. Because they filled so slowly, i assumed it could be a partial block. Maybe not.

If it is air or sludge, how do I fix it?