Hot water from vent pipe

[eckersleymark]

If there is an obstruction in feed, what is the easiest way to remove please?

 

[bengasman]

You can try poking with something like glasfiber rod, or using a plunger. If it is limescale/magnetite, it can be quite hard though.

 

[kmeeres]

Tried that. Also turned all rads on full and bled cylinder, pump and all rads. Any more sugestions please?

Blocked hot water feed, had work done lately? I thought you were talking about header tank, sorry.

I thought he meant the header tank, he also says it is continuously overflowing.

If overflow level is above float valve it could be a stuck float valve which he cannot see.
Hot water could just be overpumping possibly made worse by elevated level and expansion pipe not high enough.

You could try a magnet on the pipework to test , magnetite is magnetic so a pulling magnet would indicate a blockage.No good for detecting limescale though.