I have exact same problem with potterton boiler. Pump was replaced but 7 days later same thing happened pump not working and awful banging through pipes throughout house. Was suggested this was a 'kettling' effect due to pump not working but after new pump fitted and still a problem plumber sent an electrician to check everything assumed a short could be happening. Electrician found nothing and tried boiler again and it worked!! for 3 days!!! Now even our plumber is flumoxed! I am looking at this site to see if anyone can shed a light on this too so if you get any feedback or fix your problem please let me know. cheers debbie