Door not locking

[tinymartin2835]

Hi all, i have a Citroen c4 06 plate and im having trouble with the central locking. With the car all closed up and i press the lock button on the key fob the doors lock and then straight away unlock again and the internal light is on and the dash says FLH passenger door open. I've turned the internal light off and tried again but still the same. I've disconnected the battery and waited, refit and no difference. I've change the passenger door lock with a second hand one and it seemed to work for a bit but then started to happen again. I've operated the key fob from 2m approx away and it seems to work. I've checked all locks and all ok. Can anyone help with this fault.

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