TPMS - what do I do next?

[Greg66]

Good old TPMS. Perhaps the only thing I really don't like on the S8.

Since I've had the car I've ha a TPMS warning every time I start it. I had the sensors replaced yesterday. Alas no solution yet.

First, I bought 5 but the garage replaced four saying the spare didn't have one. The onboard display shows that it is looking for a signal from the spare, so not sure whether that (having only 4 fitted) is a problem or not.

Second, the car still isn't picking up anything from the sensors. I've tried initialising and also storing the pressures. Nothing showing - no temps or pressures.

And as if that wasn't annoying enough, I think one of the new valves is failed as my rear offside was flat as a pancake this morning.

One step forward, two steps back...

Any ideas? Should I get the fifth sensor installed? Is there a trick to initialising or to getting the car to read the sensors?