PAT fluid pump fault and consumer right questions

[Skull]

Hi, bought a 2015 hid van in November 2021. After one week the warning came on and entered limp mode. Dealer checked and code says PAT fluid and pump faults.  3 month warranty did not cover so I paid for PAT fluid refill. Still faulty and limp mode so dealer did pump refit for me. All good. 
Three weeks later I refuelled and warning light back with limp mode. Code said PAT pump again so dealer reluctantly replaced again. 
One week later I refuelled again and warning light with limp mode again.  
I had the DPF pressure checked and it passed.

Seems to happen after refuelling.  
1, Any ideas what could be wrong? Could it be DPF although fault still says pump.
2. It’s now three months on, can I insist on a return and refund as not fit for purpose.

Thanks
Graham

“I would agree with you but then we’d both be wrong”

[Sol]

Ok, so the PAT system has a 1 litre bag of fluid, should last 100k miles. It cannot measure the amount left, it only estimates it based on mileage (the ECU that is) so each time you take the fuel cap off, it assumes you are filling up, and squirts a bit of PAT fluid into the diesel tank. Over 100k miles, it should by now, be empty. The fuel cap is detected by a magnet in the lid.

You need to use Citroen Diagbox software to "tell" the ECU that the PAT fluid has been replaced, or the error will never go away. Could be as simple as that. A bag of fluid is around £70 to £100 online and just clicks-in to the pump unit, inside a black tank looking box under the drivers side rear floor, just ahead of the back wheel.