Thanks guys, really useful. How do I reset the detector? (numpty Q I know....)
Go to the garmin learning centre, into sports section, and click on the Edge 705 and it will bring a load of training videos up.
Look for the one entitled Speed/Cadence sensor. Watch it and before you say you have an 800 model the process will be the same, you will just have to scroll through your menus.
I had a similar problem to you but with a 705, I had 3 sensors (they are the same for 705 or 800's) for my 3 bikes, basicallly one of them gave cadence but didn't show speed if I tried to use it on a turbo or just spun the cranks. It worked fine picking up from GPS when on the move.
I contacted Garmin tech support and several emails flew back and forth various suggestions etc (very good tech support by the way).
In the end you have to watch the sensor immediately after you pair it, for a few seconds and as you turn the cranks you will get red and green flashes where the reset button is on the cadence sensor.
Can't remember the sequence but one is for each pass of the crank, the other is for each pass of the magnet on the wheel.
I was only getting one of the colours can't remember which one, garmin told me it should be 2 colours, tried other 2 bikes alternative red/green flashes when re-pairing the sensors with unit.
The conclusion from Garmin was the speed detection part of the sensor was broken. They asked me for the invoice which fortunately was less than a year old, so I scanned it, emailed it to them and they sent me a replacement.........RESULT!!!!
Top marks to Garmins support department!!
Love cyclechat
