[Techman]

If you've got 0.8 ohms across the heater pins then that valve obviously has a good heater and should 'glow' when powered from the heater winding of the mains transformer. If it doesn't glow then there can only be two possible causes - 1) There's a bad connection at the base on the chassis, or 2) The glass of the valve is cracked somewhere and the vacuum has been lost, but if this were the case you'd be able to see whiteness inside the glass, so long as it's not of a type that's metalised on the exterior, also it would still start to feel warm even with no vacuum.

This problem with the solder connections within the pins of these type of valve with heaters in excess of an amp is VERY common - I've had to repair loads!