Ok this fault is really common on the Series II Clio (2001-2006). I was asked to look at the problem you describe on a car belonging to a family friend. I too thought the problem had been resolved after a prod and a poke only for it to be intermittent for a while before finally packing up.
In my case the problem was a faulty motor. This is referred to as an actuator or solinoid but there is no escaping the fact it is a 12V motor. The motor is made by mabuchi and getting hold of them is difficult as they are not available from Renault, who prefer to sell you the entire actuator assembly for £50+VAT. The good news is though that these motors are available on ebay and are easy to fit. Be careful though most motors, FC-280 for example (used on Toyota/Lexus) spin in a clockwise (CW) direction and you need a CCW motor unless you modify the wiring.
Search ebay (Clio tailgate central locking motor) and if they are available fitting is really easy. There is only one screw holding the boot panel in place. Undo this with a torx driver and pull the door card of its poppers. There is one torx screw holding the actuator in place. Undoing the actuator torx screw reveals the motor in question. Check for a 1 second burst of 12V at the actuator plug/socket when the central locking is activated to confirm the motor is faulty.
Before we proceed it may be worth mentioning that a failing motor can fail in the locked or unlocked position. If the boot is in the unlocked position, turn the motor by hand until the mechanism it drives is in the extended position. Reassembly at this point will leave the boot in a locked state until you can get access to parts. Similarly, if the boot is locked and you need to open it is possible to use a flat blade screwdriver on the top of the catch inside the boot to flip the lock open.
Back to the lock..... Removal of the motor is a piece of pie. Unclip the cable and remove the grey cable socket by pinching the retaining clips. Pull of the big 40-tooth cog and pull the motor out of the assembly.
Attached to the motor is a 10-tooth brass pinion. This can easily removed from the potor shaft using a pinion puller (who has one of those in their handbag?) or a hammer and centre punch. If you do get a motor off ebay use a socket in a vice or workmate to push the brass pinion onto the replacement motor. A dab of Locktite 638 may be a good insurance policy. Reassembly should take 2 minutes....its that easy.
LeggyUna
August 2010