Hi all. I recently installed a new oil line and boiler in a property. The line is quite a run and the appliance is higher than the tank. I put a tiger loop in and used a bucket to prime the flow and return. This all went to plan and the boiler fired with no issue. I reconnected the oil line and continued to observe waiting for it to lock out which it didnt. I carried on with my commission and got my readings and left the heating on for a good hour or so to check that the radiators were all heating up etc... After a few hours I get a call from the customer telling me that the boiler has locked out. I went down there and noticed the tiger loop was empty. I reset the burner a few times and i could see it bubbling as it was purging the air from the line. After a while it was again full (bubbles had gone). i knocked the boiler off for about 30 minutes and still it was full and fired again. Now again its empty so it seems its slowly going back into the tank. I'm thinking of putting a non-return valve on the supply pipe going into the tiger loop. Am i right in thinking this? Thanks for reading!