Oil Boiler lock out

Wonder if anyone can help me with this. I have fitted a new Grant oil boiler. Everything works fine if I keep the system working. If I switch the system off for more than 2 hours the Riello burner goes to lock out when it tries to start and I have to bleed the pump to get the system going again. This would suggest an air leak but I cannot find it. I have also fitted a Tigerloop (including fitting the bypass screw to the return port)

I think I have convinced myself it’s an air leak but is there anything anyone can suggest which might point to why it goes to lock out after a period of being off.

Better to get the installer back to check if there is a fault. Or contact Grant if still under warranty if no other fault in oil line etc.
What were the analyser tests for commissioning?
If definitely air in oil pump, you must have a leak in suction side, or feed pipe from oil tank.
The Tigerloop would normally clear the air in one press of the lockout button on burner, although can need a second press after locking out if oil line also had air in it.
Is the oil tank and oil at a lower level to the Tigerloop?
Check your inlet pipe connection near Tigerloop.

Thanks Reject, I think I'll just get the installers back in. I'ts working at the moment by setting the CH and HW controls to come on and off within a couple of hours of each other just so that the pump runs regularly for 10 minutes or so during the night. But of course that is not a long term solution.
The bottom of the oil tank is probably just about level with the Tigerloop and there is about 400L left in the tank. If you take the bleed screw on the pump right out oil does flow and of course if you start the burner there is plenty of oil from the pump. That is why I'm thinking it is air in the line. I was only asking in case there is something else which can stop the burner igniting but really once I bleed the oil it works so I think I have answered my own question. I'll get them in to sort it.
Thanks

Capacitor on burner motor could cause failure for motor to turn sometimes.

Or combustion setting on boiler wrong causing failing on cold starts. This would explain boiler starting when warm, but not after 2 hours or more of being off

When it is running, do you see bubbles in the tiger loop?
After a break, is there still oil in the tiger loop?
Does the tiger loop have to lift oil from the tank or is it just for de-aeration? If it lifts, how high and how far?

What model boiler isit

Is the tigerloop slightly higher than the burner like it should be. Bob