Start fault multiple ignition key turns to start car

[Telf]

Hi all,
I have a 2005 1.9TDI with a weird fault.

It basically intermittently wont start.

It has had a new starter motor recently and all was well for a month or so. Now it has developed the following symptoms:

Turn the ignition key.
The glow plug lamp fails to illuminate (even for a second) and then it wont start only cranks.

If the glow plug lamp flashes on the car will start no issue at all.

I thought oh ok this must be glow plug related so hunted down the glowplug relay under the fuse box - replaced it but no joy.

I then rooted around and noticed when the glow plug lamp flashed a relay could be heard under the steering wheel - so i found that, you can feel it click when the lamp comes on (followed by a start)- its a slim relay the same as the horn so swapped it - this didnt help. ( its labelled as 51 on the relay board) which seems to be fuel pump related.

So now the car only starts every between 5th and 50th! turn of the the key ( no exaggeration). If the glow plug lamp lights even briefly it always starts ( the the relay can also be heard and felt to click).

Now its warmer days I've also noticed even if the engines hot (so shouldn't need glow plugs) it still wont start.

I've also noticed my basic code reader wont connect unless the car has successfully started - so is there an ECU issue.

I'm at a loss tbh and ready to get rid of the car, its turning into a waste of life.

Has anybody ever seen a fault like this on a Mk5 TDI before? Its a 2005 registration.

Thanks

[Crasher]

You need a code read and I expect you will see a terminal 15 or terminal 30 error stored. What is the VIN?