Have you considered an email to Raymarine Service ? I found that they were prompt and pro-active in various situations.

I had a Airmar speed transducer pack it in not that long after installation (but just out of warranty). When that happened I found some info on the www about how to test the transducer which I suspect is what Charriot is referring to. Mine was hard wired. I guess with the wireless version that introduces another potential cause of failure ie something wrong with the transducer itself and/or something wrong with the wireless functionality. Not sure how you would test the latter.

Re in-hull depth transducers. My depth transducer is actually a through-hull but mounted internally to avoid having to put another hole through my boat. Mounted in a cut off piece of PVC pipe using Sikaflex sealant to stick it to the inside of the hull. Fill the (now sealed) pipe with liquid and the transducer will work from inside the hull.

Thanks for your replies, particularly Matt, I like your ingenuity.
cleaned the hull - no difference.
Rang Raymarine tech support.
They advised that because I could read the heading and speed that the sounder was knackered.

I then ordered a new in-hull transducer - sadly it still didnt work.
At which point I knew it wasn't the transducer and therefore must be the transmitter.

I then triple checked the connections and bent the luggs on the transmitter box to make better
contact with the the heading, depth speed and power in plugs.

It subsequently worked.

So the transmitter has battery's. These batteries had enough juice to run the speed and
heading but not enough for the sounder which I think is power hungry.

So beware, just because your heading and speed sensor are working.
It doesnt mean you have power to your transmitter unit.

On the super positive side Whitworths said they'd give me a credit.
I've spent tons of money with them so am pleased they relaxed the rules for me.

So bit of a battle but its fixed now