Greetings, I had my buried 300 gallon heating oil tank replaced 9 years ago. Our downstairs heat pump has an oil fired back up. In November when the temp dropped, the oil furnace wouldn't fire. Long story short, discovered water in the tank. The tech jumped the burner pump and we pumped 6 gallons of water through the lines until he reached oil. Replaced the oil filter and nozzle and the furnace ran fine. Knowing that the intake line is off the bottom of the tank, the next day I fastened a hose on to a long rod so the hose would come within 1/2" of the bottom of the tank and manually pumped another 6 gallons of water out (12 gallons total). Geez, the tank is only 9 years old. The furnace ran fine last March, now 8 months later it has 12 gallons of water. Best case, knowing the intake tube was 6 gallons from the bottom, at least 6 additional gallons entered the tank since it ran fine in March. Here's where is gets odd. For the last 2 months, every other Saturday (4 times total) I've dropped the same rod/hose in the tank and pumped exactly zero water out. None, it's all pure heating oil, and we've had plenty of rain. While I used to keep the tank full during the off season I've probably only had the tank 1/3 to 1/4 full every off season since the tank was replaced. Is there any way possible an underground tank can accumulate that much condensation? I'm stumped. Sorry for the long post. thanks

 

It seems really odd there would be that much water in the tank. I cannot believe it came from condensation. All I can think of within reason & this is a real long shot, is at some point the ground became saturated & water seeped in around the threads. Does the tank have a flip type fill cap? If so, maybe someone at some time left it open. I do suggest you get some water detecting paste & keep an eye on the tank.