Fuel tank breather issue? Petrol pump keeps cutting out when refuelling

Hi all.

I have a 2017 C3 Flair 1.2 petrol. Recently, I am having issues filling up at petrol stations. Where I can only get around £5 of petrol in the tank before it cuts off, as if the tank is full, but in reality it is no where near full. Take the nozzle out and and try again, and can only get dribbles of fuel in (again, as if it were actually full). I have tried this at 4 different petrol stations now, so it is definitely the car rather than an a faulty pump at a petrol station. It does this at every fill up, it is not an intermittent issue. The car has had an easy life, under 30K miles, never in an accident, full main dealer service history.

I suspect the issue related to the tank breather / venting system. I.e. when filling up, the air displaced by the fuel being added, has no where to go, causing pressure to build, which in turn is causing the fuel filler nozzle to cut out. I have concluded this, as at last fill up, when it started cutting out again, I used my finger to hold the flap open on the filler pipe (where the fuel pump nozzle goes) in order to allow the pressure inside the tank and filler pipe to equalise, I was then able to continue filling again (I couldnt before I held the flap open).

I got under the car today, to look for a vent pipe to try and check for blockages. I found what I think was the vent pipe. A smaller diameter white pipe that runs next to the larger main filler pipe, from the tank, back toward the main filler area (where you would refuel). I managed to take the smaller diameter pipe (the one I think is the breather / vent) off where it connects near the filler, and I was surprised when some fuel come out the pipe. Not loads, but some. This made me think two things...

1. Could the fuel in the vent pipe be causing the issue (i.e. blocking the vent pipe)?
2. How on earth did fuel get into the vent pipe in the first please? Is that normal?

In order to move forward, any ideas on the above 2 points or the following?

a. How would I go about diagnosing what the issue actually is?
b. Is it likely to be the vent I have found, or are there any common issues it could likely be?
c. Does anyone have a link to a technical diagram that shows the filler pipe, tank, breather pipes etc. for my specific model?


Thanks in advance all!

Roy

Yes, that is the vent pipe. It should vent to atmosphere at a point on the filler neck above where the end of the bowser filler nozzle enters the filler neck.
The theory is that as you fill the tank with petrol, displaced vapors in the top of the tank move up the vent pipe, past the nozzle and out the filler neck. If there is a blockage in the vent pipe, fuel wont be able to enter the tank fast enough, causing a back flow of fuel and the bowser will cut off. If you manage to get fuel to flow at a slow enough rate and you completely fill the tank, all the way up the filler neck, fuel will then run down the vent pipe to the blockage and fill the vent pipe.
I have never had cause to look at the vent pipe arrangement so unfortunately I cant tell you what would be involved. I'm not familiar with the later models of the C3 but there should be access to the fuel pump and perhaps limited access to the top of the fuel tank by removing the back seat and the hatch cover? Otherwise you may need to remove the fuel tank.