worcestor 25si

[gbutch]

boiler about 8 yrs old works ok but when it fires up it makes a vibrating sound from the back of boiler where the copper coil is ,if you touch the coil the sound goes away but allways comes back
yours gb

 

[bengasman]

pump or fan worn, probably fan

 

[gbutch]

it wasn't peanuts 8yrs ago,it's not the fan don't think it's the pump because the pump continues circulating hot water for heating after the burner shuts down and the vibrating sound only starts when the burner starts and it comes from the copper coil at the back of the boiler
yours gb