Heat pump water heater says my condensate line is blocked, even though clear

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Pictures of my setup here  http://imgur.com/gallery/rCs8R

The unit is a Rheem "Prestige" heat pump hybrid water heater.

When I originally hired a plumber to install the heater, he used PVC pipe for both the primary and secondary condensate line outs, connected together further downstream with a tee.

The water heater alarmed that a condensate line was blocked so I removed the fixed PVC piping and replaced them with transparent vinyl tubing with removable garden-hose style connectors so I could see what's happening. I manually poured water down the line to confirm they're not blocked. Everything drains smoothly.

I let the vinyl hoses hang off of the unit into a bucket for a few days, rather than the normal drain, and the unit never alarmed while gradually filling the bucket with water. But now that I connect them to the drain pipe it alarms. There's no obvious water blockage.
Could it have something to do with the pressure of being looped into a longer, narrower PVC drain pipe (third picture)? Seems unlikely but I'm out of ideas.

Water is definitely not backing up into the unit.

Any other things to try?

[Livethedream]

I would contact Rheem customer support by phone and see what they say. Try searching online and see how much it would cost to replace the sensor if feasible.

[BudgetSlasher]

I installed an 80 gallon version last year and the drain lines are simply placed into a stand pipe (like a washing machine would use). I have had no problems.

Here is the install manual for the 50 gallon version available today via home depot: https://www.homedepot.com/catalog/pdfImages/2b/2b4d73bf-5db1-4e11-871e-edab5c91b119.pdf

Pay special attention to page 7.

Primary condensation (3/4") to open drain or outdoors

Secondary condensate tubing (3/8") to open drain or outdoors

manuals for older versions said floor drain instead of outside.

In light of light of your experience with proper function with an open drain (the bucket), my experience with a stand pipe, and the manual I think you are right to be suspect of the PVC line. If I were you I would covert the PVC to a stand pipe with trap, run the lines to a floor drain, or run the lines directly outside.

[a_scanner_brightly]

Thanks for the replies so far.

There have been some developments.  Letting the hoses drain into a bucket eventually did cause a condensate alarm as well.  It just takes more time (~3 days) to trip than if the hoses are connected to a drain (<24h).

@BudgetSlasher would you be willing to share a picture of your condensate line connection at the WH?  I have some reason to believe that it needs to go directly down 90 degrees and also have an ID as close to 3/4" as possible.  The plumber originally installed a 90 degree PVC elbow but it went through a male-to-male adapter to be threaded into the WH, so I wonder if the extra distance introduced by the male-to-male plus the inner diameter of the PVC not being quite 3/4" is putting back pressure on the sensor.  (And if the "open drain" aspect of my setup is a red herring)

If that doesn't work I'll eventually break down and call technical support and hope they say something useful while exploring replacing the sensor, as @Livethedream suggests.

[big_owl]

I have a HP water heater as well.  No problems so far...I just run my condensate line to a condensate pump which then pumps the water to a drain in my basement.  Not sure how they determine that your line is plugged...whether it's pressure or some other means.  I'd call tech support and scour the internet, there's probably a sensor that's gone bad.  Might be an easy fix though, or more expensive if an input on a control board had gone bad.

[BudgetSlasher]

@BudgetSlasher would you be willing to share a picture of your condensate line connection at the WH?  I have some reason to believe that it needs to go directly down 90 degrees and also have an ID as close to 3/4" as possible.  The plumber originally installed a 90 degree PVC elbow but it went through a male-to-male adapter to be threaded into the WH, so I wonder if the extra distance introduced by the male-to-male plus the inner diameter of the PVC not being quite 3/4" is putting back pressure on the sensor.  (And if the "open drain" aspect of my setup is a red herring)

I've attached (or at least attempted to attach) a picture of where the drain lines attach to the water heater. You will have to pardon the use of zip ties over hose clamps, it is something I meant to correct, but then realized clamps were not strictly necessary in such a low pressure situation.

Mine does not go down directly 90 degrees and it has not been an issue. The only issue I had with the drain lines early on was that they need to run pretty constantly downhill. If they wind up with a rise enough to fill the hose completely with water (mine sagged between anchor points on the way to the stand pipe) there can be an issue.

As for 3/4, I used it for the primary drain line, but as you can see for the emergency overflow my heater has a smaller port and thus I used a smaller hose.

I had always assumed that since the hoses were meant to be open to air (without any real pressure to speak of) and the internal part is likely an open drain pan the sensor for a drain blockage would be a internal water level sensor in the drain pan rather than a pressure sensor, but I have nothing to prove that.

When you have done the bucket test, did the ends of the lines ever get below the water level in the bucket creating a seal? Also when the alarm goes off can you tell if water has been flowing through the overflow (higher) drain hose in addition to main (lower) hose?

On a side note my basement dehumidifier, which lives next to my water heater, occasionally develops a slime mold blockage in some part on its drainage system that I have to clean once a year. So far I have not had this issue with the water heater, but I would not be surprised for it to crop up at some point.

[Just Joe]

Find out how the system senses water. It might be a sensor that needs to be cleaned or replaced. My car has a sensor that tells me when the windshield wash is low. I've seen these fail so that even if the reservoir is full, the light still claims it is empty.

I wonder if it is a similar sensor in your appliance. I don't think it is a float but a couple electrified probes charged to mV (milli-volts). If there is some continuity then there is fluid there.