gushing noise hw only

[micey]

Have a problem with hot water only that is doing my head in
Gushing gurgling from hot water only, put ch on perfect no noise,
The water heats up ok but bloody wakes me up!
Its a 2 pipe system y plan vented, potterton suprima 60,grundfos alpha pump,(done same noise with old myson pump)
It has done it for a few weeks now, but left as had to change rad so would investigate then,
Have changed rad, and found diverter valve half seized,so took apart and cleaned hoping that could be fault, but no still the same,
It sounds like its coming from hot water cylinder gurgling etc,could the coil have an hairline crack? but water out of taps fine?
I have had the pipes off too the coil and blown through ok ? and none of hot water tank coming through coil,
sorry its a bit long winded!

 

[hi-spec plumbing heating]

what is the tank stat set to ?

 

[micey]

It is set to 62 deg usually i just checked as it was on 55 i might of knocked it earlier,

 

[Gasguru]

Perhaps a little traped air in the coil - should be an air vent on the top primary connection on the cylinder.

 

[micey]

Thanks for the replys
No air vent but is a drain other side of valve so will put valve in mid position tomoz and put pipe in bucket and be careful not to let air in,