Central locking not working (not CCM)

[Eddie4]

I started this thread as seemingly all threads discussing faulty door locks blame the Comfort control module/area (as it is common for water to leak through the pollen filter and flood the electrical box/connections. I have a 1999 1.8T estate.
My problem is that all 4 doors have stopped working (no central locking). I still have to disarm the alarm with the key fob, but then manually open doors either with the key or unlocking from inside the car. When I use the lock/unlock buttons on the drivers door, only the boot lock opens/locks.
So immediately I thought I had a problem with my CCM (as this is such a common problem). So I accessed the CCM and electrical junction in the passengers foot well, and these looked as good as when the car left the factory. I checked for loose connections, and even used a spare good CCM to test if it was a failed ccm. I used the key to see if the central locking would function as I know the spare CCm would need programming.
So my question is, does anybody know what else could be responsible or explain all doors stopping working, including the petrol cap? Only the rear boot latch still works, and there is nothing obviously wrong with the CCM and/or connections (bone dry).

Other information possibly relevant:
1) Power windows still work
2) All fuses good.
3) Coincidentally this problem developed around the time of my battery dying. Have since got new battery.

[JohnPierpoint]

My 03 Passat has just developed the same fault. As with the original poster, the battery appeared to be on the way out (low voltage), so I've had it replaced. However, this hasn't fixed the problem. I can hear relays in the CCM clicking when I use the fob to unlock, and can hear a whine from the doorlock motors, but nothing happens. The CCM appears OK (it was repaired a few years ago - with lots of help and advice from people on VWAF - and moved to on top of the passeenger side carpet to prevent any more water damage).
Does anyone have any ideas?