works fine when out on the bike but i tried to use it on the turbon trainer today and although it is showing ‘connected’ to the speed and cadence sensor when i start pedaling nothing is showing on the speed and distance…am i being a numpty and missing something here?… help please..

Same rear wheel? I use a separate wheel for the turbo with a turbo specific tyre so the spoke magnet is attached to that. Sometimes I switch it to the road wheel and forget to switch it back and I see what you see.

Are you sure you have the magnet lined up? Even if the sensor isn’t picking up the magnet when you are outside you will still get a speed readout from the satellite connection.

its a specific turbo bike with same wheel as it always stays on the turbo, i just change the bike set up in the settings for the turbo bike

it’s a sign to say get off the turbo and get outside to ride.

Anyway, have you checked the magnets on the wheel and crank is aligned and activating the sensor? The little reset button flashes red for one magnet and green for the other.

EDIT – assuming Garmin GSC-10 combined speed/cadence sensor

Ditch the 800, get a dongle and trainerroad?