is it always the tank causing the low level warning? On my last mig I kept getting it and recall ruling out the expansion tank sender and assumed there was another sender somewhere and an airlock. It coincided with the heater being only luke warm. Both both problems were alleviated simultaneously by a fairly savage descale.
Yep, sort of... It's the level sensor in the tank

I think the result you had was down to the de-scale

Hmmmm.
Perhaps this is falling on ears who do not wish to hear, but I lift the bonnet on my car at least once a week to top-up washer fluid, run a rag around the bay etc......... Who would HONESTLY pull over the very instant the MID said 'Check Coolant Level'?
I'd wager nobody who really knows their car would.
We would keep an eye on the temp gauge, have a look-out for steam and drive on until we reached our destination and THEN have a look...... wouldn't we?
I would for exactly the reason you state. Well, not instantly but ASAP

I keep on top of my cars (generally) so would know that the warning coming up was for a reason

In fact, on my saloon I had this happen on the way down the A3 to go to a funeral... Pulled over and sure enough coolant was low due to a failed HBV. Managed to limp it to the funeral and the 160 miles home though, once I'd worked out what CC setting I needed to minimise the leak

Probably saved the engine at the speed I was going
