Furnace Condensate Pump Check Valve

We have a high efficiency furnace with a Beckett CU141UL condensate pump.

In the winter, it pumps about two liters of water per day through a 3/8 inch I.D. vinyl tube, running 8 feet vertically to the basement ceiling and then 15 feet horizontally out of the house.

The pump began to frequently (and noisily) cycle, 24x7. There were some entrained bubbles in the tubing, and they would get pushed outwards while the pump was running, and fall back inwards when it stopped.

There is a black plastic fitting connecting the pump to the tubing. This is a check valve, screwing into the "1/4 inch MNPT" hole. The threaded fitting is actually 1/2 inch on the outside of the threads, 18 threads per inch.

The purpose of the check valve is to prevent back flow. It wasn't working. I removed the hoses and fed them into a plastic tub. I unscrewed the fitting (7/16 inch open-end wrench) and looked through it. The little flap inside was twisted and would not completely close.

I could not locate spare parts for the Beckett pump. New pumps are around $100, and the pump itself worked fine after some disassembly and cleaning. Where to find a check valve? Local furnace repair shops do not carry the valves, just pumps, the same as the big box stores. It would be a terrible waste to buy a whole new pump!

Fortunately, the CV-10 check valve (Item 599065) from Little Giant Pump, available through Amazon, worked fine. The old valve had some plumber's sealing paint over the threads - the CV-10 comes with an O-ring. The inside diameter of the through-hole is 1/4 inch on the old valve, and 3/16 on the new valve, but the smaller orifice is feeding 20+ feet of tubing, so the extra constriction matters little.

I've also learned that it is a good idea to connect the spare "input" port on the condensation pump to a shop vac every year or so, so suck out all the crud that accumulates in the pump and in the furnace. This might have saved the check valve.