Furnace technician spent 5 hours trying to fix this problem (to no avail):
At start of season, I purge my single-line oil system by turning on pump and open the bleed value, to fill the line with oil and get rid of any air.
I have a tank about 4 ft below the pump at the furnace, with the single copper supply line going across the top of the basement, about
6 feet above the pump. A standard filter is in the line 3 ft from the pump. The filter was changed, along with the rubber lid gasket.But somehow, air gets in the line. After purging, it's OK and starts nicely and always and continues to run. But when left overnight, air enters the line and the shutoff kicks in.
When I then open the air bleed to purge the line (with the pump turned back on), foam comes out for a lengthy period of time.
I'm presuming that during the night oil is draining back down the supply line into the tank, which is below the level of the pump, filling the 20 ft supply line with air.
Worse, when I try to bleed or purge the air out of the pump and line, what comes out is intermittently foam, then some fuel oil with a bit of air, and occassionally straight, clear tawny fuel. I can bleed out a half gallon of fuel, but the problem remains.
Can the problem be solved by putting some sort of check valve on the supply line near the pump, to stop the back flow of oil back into the lower tank? Where do I get one of these check valves? What do I ask for?
And of course, from reading the literature on this, many are going to say that I need to simply create a two-line system, to send the excess air back into the tank.
But since the system runs well when there is no air in the feed line (after extensive purging), I'd like to at least try a supposedly cheaper check-valve in the line first..
The tech guy said that this was the weirdest, most difficult and enigmatic problem he's ever encountered.
What are the (probably many) soutions to be tried? I'm at whit's end.
--John