Tiger loop is empty

[ptarka]

Hi guys,

I have an oil fired boiler with a tiger loop. The pipe run is about 8 meters and the burner is about 4 feet above the bottom of the oil tank.
I have lived here for 2.5 years and the boiler and tiger loop are 11 years old. Ever since I moved in, if the oil level in the tank gets down to about 1.5 - 2 ft the tiger loop empties after 8 hours or so of not running. The boiler will lock out and usually I can get it running after 3 or 4 goes on the lockout button, but not this time.
Is this situation normal?
I understand tigerloops have non return valves in them? Given this I would have thought its not possible for the oil to run back to the tank while the boiler is off?
Also, I have read about the bypass plug in the return port in the pump. Is it possible this has not been fitted?
Any help would be great as we are getting a little chilly now :O)

Thanks in advance

 

[oilhead]

Without examination, it is difficult to diagnose faults on tiger loops.
When it is running, do you see any bubbles? Can you see the fuel running into the return port? Has the pump vacuum been checked?

 

[dcawkwell]

Air leak in the fuel line joints somewhere on the system.