A service plumber from a plumbing company had called me from a job site and said his customer had a clear radon sump cover on the sump basin and it appeared that the pump was running, but not removing the water. When the plumber was looking into the sump basin there was bubbling and turbulence. To complicate matters there were two pumps in the basin, one primary pump and one battery back up pump, both discharge pipes were coming up through the cover and were tee-ed together. He could not tell which pump, or if both pumps were running as both discharge pipes were vibrating.
As a process of elimination I asked the plumber to unplug the primary pump. He did and reported that nothing had changed, there was still turbulence and bubbling action going on in the sump basin. I then asked if each pump had its own check valve and sure enough, they did.. The plumber asked “why two check valves?” and I explained that without a separate check valve for each pump there would be water recirculating from pump to pump.
As it turned out the primary pump had a stone jammed in the impeller and the check valve for the primary pump had a broken flapper. The battery back up pump was just recycling water through the path of least resistance, the primary pump.
The plumber did mention that the alarm on the battery back up system did not work. Some battery back up systems have an alarm with a “silence mode”. I asked him to check the alarm to see if it was set to this “silent mode” and it appeared that it had been “silenced”.
With the rock removed from the primary pumps impeller, a new check valve installed, the alarm mode set to “audible” and the radon cover resealed the homeowner is back in business. Fortunately the homeowner had heard a different noise coming from the area where the sump pump was located and took action by calling a professional plumber. The service plumber had never seen this type of installation and called us for troubleshooting advice. A Job well done. Mysterious bubbling sump pump solved.