Edge 830 - Power2max NG; No Wattage data;

Is it connected as a power meter...the dumbbell symbol?  Does the bar across the top of the home screen shows the dumbbell solid and not flashing?  Can you go into the sensor page and do a calibration?

Paired through BT or ANT+? (You can do both, check its type under the sensor details) I recommend to use only the ANT+ protocol (and check with the Power2Max mobile app your NG settings, there is ANT+ ON/OFF toggle and must be switch on. You can do a factory reset also with this app to reset your NG, and maybe You need update its firmware also, probably these will solve your problems)

Thanks Luko, I'll give that a go, I think its BLE connected but no idea, I'll have another look before I head out today, it's annoying though!!!

it is, it's a solid dumbell and I can calibrate it - which is unusual as it asks me to unclip and not pedal....but yes, that works

I agree with Luko79, ANT+ is generally more reliable.  When you first pair a sensor that has both BT and ANT+, you'll see both options so, select ANT+ then.  You can try forgetting your PM on the 830, then reconnecting it as ANT+.

The P2M zero offset calibration (or of other bike power meters) must do unclipped like when You are zeroing a bath scale before You are standing on it (this procedure is "showing" the powermeter what is the 0 point when there is no torque applied on the cranks). It is different than the indoor trainers "spindown" calibration which needs to pedal to a given speen and stop the pedaling. BTW the P2M has autocalibration (when You are coasting outside for a 3-4secs with non-rotating legs) so dont need to do this manual calibration before every ride (only for indoor training it is recommended because there usually You cant coasting except on trainers with downhill assist like Tacx Neo)

Is it a completely new NG, never used before? Did You register it in the app with that code on the red label? (Or is it a factory installed P2M into a new bike, like with Cannondale bikes?)

If You try to rotate the cranks with hand only then You wont get power (at least if You do it smooth) only cadence. The P2M's ANT+ sensor has a 5-6digits number as ANT ID, its BT sensor has a longer name with letters so easy to recognize which one is which. And after You identified , disable the P2M BT sensor in the 830 and leave the ANT+ sensor enabled only.

I've got the NGeco and it's reporting power.  A stupid suggestion but make sure the firmware is updated on the NG.

Thanks Luko - Appreciate the time you took to write that.

It is a new NG, it came fitted to the Cannondale, but I registered the red label thing in the NG App, that seems to be ok - The app says I'm registered and it can talk to the crank. Through the app I have done a factory reset and reinstalled the latest firmware.

The 830 picks up cadence (though I dont ask it to, but it always appears in my strava) so I know that part of it is working; I have swtiched between ANT, BT and both, it says calibrating successful (usually flashes up some numeric value 0.8xxx)

After I add the sensor in the 830 I follow the script and add every power value I can to the screen, I see the cadence value, but power continues to read as 0w ... 

Do you think my crank is broken? I cant think of any other reason!

ah! ... hang on....power upgrade on the app, never knew that was a thing, I'll try that!