What is causing the air in the inlet line?

So I've just tried a simple approach to this problem.

I watched an air bubble get drawn into the fuel line from the boiler unit itself, after it had stopped a burst of heating. The next time it would try to fire up, it would get this air bubble drawn straight in and cause lockout.
Looking in the manual, I saw that the fuel line is meant to rise up past the desired height, and then descend a couple of inches to the valve. Mine didn't ....... so I got a shoelace and tied it up so now the highest point is an inch to the left of the filter; this is where the obligatory air bubble will now rest. The boiler can now receive a better flow of oil when it fires up again, and it seems to be working, at least better than before.

Nilotic
September 2010

i dont know enough about your system but a leak in the suction line will allow air to enter the system and still not leak fuel out. a vacume test would confirm this. is it a lift application? what kind of fuel pump? what kind of burner and type of furnace?

P
April 2009

You don't say what make of boiler you have, or if the oil tank is below or above the boiler, if the oil filters have been cleaned or repalced, I suspect that your boiler is above the tank, in which case you need to look at the flexible oil hoses at the burner, as if even slightly cracked, thesy will not leak oil, but will allow air to be sucked in, as the system is under a vacuum, other causes poor connections on oil line above height of oil or faulty non-return valve at oil tank, or if boiler is HRM Wallstar, faulty Fire Valve (it's special with built in NRV)

Boiler Repairman - Ipswich
April 2009