Ok have Removed the Global Variable HeatDemand_GuestEns from the Dashboard App.
Refreshed browser.
Checked Var removed from dashboard.
Added Global Variable back again in the Dashboard App.
Checked Global Var NOT in Dashboard, refresh browser - Global Var back - added as a Tile Variable Boolean
And it is displayed as TRUE when the actual variable is FALSE.
Fortunately the HE rules see the variable as FALSE and do the right thing only the HE Dashboard is stubbornly displaying TRUE regardless of the actual variable state.
I use it to check Heating demand is working correctly.
Will try creating a new Dashboard now with the same Global Var and see if I can repeat the issue.