How low to let oil tank go before filling it up

How low is it safe to let oil level in home heating oil tank go before filling it up again without running risk of airlocking the system

Oil tank isnt sitting on ground but is off ground sitting on about 3-4 cavity blocks

Thanks

I usually let it go to about 6 inches from bottom before filling up.

check the level at which the pipe comes out of the tank. Some are higher than others. You can use an old sweeping brush handle then to check the level in the tank and compare the two.

Also keep in mind that over the years you will get a sludgy build up deposited in the end of the tank and it's best not to allow that muck into the burner.

so try not to let it run out, and if it does don't tilt the tank.

woodbine said:

Also keep in mind that over the years you will get a sludgy build up deposited in the end of the tank and it's best not to allow that muck into the burner.

Click to expand...

On that note, is it just a matter of time before that build up gets to the same level as the pipe? Should you get it emptied before then or what?
My tank is around 3 years old and there's a fair but of muck at the bottom.

If the base of the tank is at a higher level to the input to the boiler, then you can let it go down to a few inches- its driven by gravity only. Beware of silt and dirk in bottom as mentioned.

so try not to let it run out, and if it does don't tilt the tank.[/QUOTE]

We tilted the tank as we were close to running out over a weekend with no delivery possible, no problems with this. Just be careful not to dislodge/knock the feed pipe.