Banging when boiler shuts down!

[simplesi]

Hi everyone, wonder if anyone knows why my old baxi boiler make a series of bangs after shut down? There is then a short pause and then it reactivates and dumps some water in the surplus tank in the loft for five seconds. System is hot and working well otherwise. Boiler is over ten years oldbut working well serving eight rads. Any thoughts much appreciated

 

[namsag]

Boiler either doesn`t have a pump over run when it should or Boiler stat is on its way out ,ok while pump running as it gets gets rid of heat but when it turns off too much heat is left sitting there and it is turning to steam and shooting up vent pipe

 

[baxpoti]

Sounds like a a pump over run problem

 

[simplesi]

Thanks thats interesting, i have fitted a new pump one year ago because it was noisy when running. I run this pump on full no 3,