[David McIntyre]

On my Canter truck it is low vacuum warning. Some weeks vacuum holds ok, some weeks it goes in 3 or 4 days.
No problems. Both clutch and brakes are "heavy" till it pumps up - mere seconds.
I always park the truck in 1st gear.

[Comber]

Thanks for all this information - brilliant.

[mightymike123]

Or, if it's been sitting too long with a not full fuel tank. moisture gets into the fuel filter. Undo the butterfly nut on the bottom of filter and bleed some into a container. Retighten and pump knob on top to repressurise.