Overflow pipe off heating system

Hi
Has anyone come across this small bore copper pipe that runs off the central heating. The pipe runs up to the roof space and terminates in the central heating small feed tank. It seems to act as a vent or overflow for whenever the client turns on the hot water. The coil heats the water and as it heats up, it causes water to go up the pipe and start to fill up the central heating feed tank. This causes a problem because it causes the feed tank to overflow on a regular basis.

Any thoughts would be useful

Thanks

Paul

1. The boiler should (unless it is a system or combi boiler) have a 22 mm vent pipe running from the boiler to an inverted "J" of pipe with its open end above the F&E tank.
2. If that pipe is being used as the vent pipe then:
2a. It is too small in diameter.
2b. Goes through a valve which could close off the direct route from boiler to F&E
2c. It is dangerous with respect to either problem.
3. It may be that vent pipe is a different pipe, not shown in your photograph. In this case the 15 mm pipe is being used as the feed into the boiler's primary circuit. If this is the case:
3a. It still shouldn't be pushing water into the F&E tank.
3b. If it is, then there may be an issue with the pump being set to too high a speed, or some other pipework problem causing the issue.
4. You need to trace and publish photographs of the runs of pipework between F&E and the boiler's primary circuit for a more definitive answer.

Looks like that 10mm pipe is what passes for an open vent.
The pipe running along side is probably the cold feed.
Not surprised it pumps over! Needs urgent attention
Get plumber to it a.s.a.p

DIY job and potentially dangerous if the microbore blocks , if it isn’t already !!