Hot water venting into header tank

[Stuf75]

Hi guys. I have an issue with the header tank in my loft being full of hot water. The vent from the cylinder goes into the cold water tank so it’s not coming from there. There is a vent pipe that comes from what I am assuming is the hot feed to the cylinder coil (50mm copper looks like it come from boiler) all the time the boiler is on the pump runs and it pushes hot water into the header tank even if the boiler isn’t firing. Is it normal for this to be vented? Am I just seeing pump over run which should be going through a bypass but is just dumping it into the tank instead?
im not sure what system it is all I know is it’s oil fired and was installed in the 60s and the previous owners Dad considered himself a genius and has fiddled and altered all sorts all over the house and generally screwed everything up ( I will spare you the story of the electrical repairs he made, suffice it to say disconnecting the earth rod isn’t the best way to stop rcds tripping).
Any advice is much appreciated.

Stu

 

[exedon2]

In simple terms no it should not be pumping over the top. Indeed needs urgent action to stop it happening can (and probably has) cause all sorts of problems.
Clear pictures of boiler / pump any motorised valves and pipework to cylinder would be useful.

 

[Roy_66]

Stupid question first: How many header tanks are there? (Does the boiler have its own header tank, or is it pressurised from the mains - can you see a filling loop and a pressure gauge)

Cheers,

Roy