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Strange Problem with Hot-Water Recirculating System

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AidanDanner

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Thank you for all this advice! To answer some questions:

We did have a loop installed, with a dedicated return line (and therefore we don't have one of those black sensor valves under the sink). This hot-water recirculation pump was installed at the same time that we were doing a whole-house copper re-pipe, so it was cost-effective to have a loop installed . My understanding was the loop was installed to BOTH bathrooms (the master bathroom and the guest bathroom), but honestly I haven't really confirmed that guest bathroom is indeed in the loop.

I will do this first-in-the-morning test tomorrow and report back the results!
 

AidanDanner

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Here's a probably dumb question: which way is the pumped water supposed to flow? Entering the pump from the right, exiting the pump to the left? Or the other way around? I ask because I just today noticed the arrow on the check valve, pointing to the right rather than the left, and this is different from how I always envisioned the water flowing. (I have not removed the check valve; it's how it was originally installed ten years ago.)
 

hukre

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Here's a probably dumb question: which way is the pumped water supposed to flow? Entering the pump from the right, exiting the pump to the left? Or the other way around? I ask because I just today noticed the arrow on the check valve, pointing to the right rather than the left, and this is different from how I always envisioned the water flowing. (I have not removed the check valve; it's how it was originally installed ten years ago.)
A hot water recirculation system with a dedicated return line is normally designed with the pump in the return line at the water heater, so the installation in the photograph is ok, water flowing into the pump from the left, then going through the check valve and returning to the tank (you can see in the picture that it is a swing check valve with the hinge on the left, which is where the water enters).
We have to make sure we don't get sidetracked but review the facts: The homeowner states that the system has been working properly for about 10 years, which means that the system as designed and installed is ok. Then something happened and there is practically no flow anymore in the dedicated return line. This is what we have to focus on.
 

hukre

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My earlier comment was made under the assumption that you know that the pump is actually running and not just plugged in the outlet. Your pump timer could be malfunctioning and shutting down the pump when it is supposed to be running (just because there is power in the cable to the pump doesn't mean it is running). Using any cheap stethoscope would tell you if the pump is running or not if you can't hear it when you put your ear against it.
 

AidanDanner

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I can definitely 100% confirm that the pump has power and is running. Its makes a very distinct noise, whenever the timer kicks in, or when I manually turn it on. (It's the exact same sound that the old pump made, when running. I suspect the old pump was probably still totally functional, and did not need replacement.)

I performed the test that was asked of me. The pump itself becomes warm, but the pipes on either side of it don't warm up very much at all. So I suppose this would suggest a blockage of some kind, somewhere in the dedicated return line? Anything I can do about that, or is it time to call a plumber?
 

hukre

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There is the remote possibility of an airlock. Questions: Is the pump at a higher or lower elevation than the master bedroom sink? Is there anywhere a vent on the dedicated return line?
 

hukre

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After giving it some more thought, I believe that an accumulation of sediment on the bottom of the tank restricts the flow at the drain outlet of the tank, therefore greatly limiting the flow in the return line, also in view of your earlier post where you mention that when you drained the tank, there was barely a trickle coming out. Emptying the tank again and flushing it thoroughly may get rid of a lot of the sediment. When flushing, make sure to close the ball valve in the return line (valve with yellow handle at bottom left of the photo) so your flushing the tank and not the return line.
 

AidanDanner

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Okay! I will re-attempt flushing the tank this weekend. Will report back results. (As to your other questions: I don't know if there is a vent on the dedicated return line. I don't see anything like that on the line that is visible inside the house. As for the elevation of the pump, the pump is slightly higher than any of the house's sinks.
 

breplum

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We always install tees with hose bibbs on both sides of the pump.
I have run into dozens of air entrapped pumps in this exact situation.
The exact symptom you describe is why we add the hose bibbs, to bleed out air using washing machine hose into a bucket.
You can get the same effect by opening the unions at the pump but it is a complete water mess and will likely splash on your pump electrical.
Put in air bleeders.
 

hukre

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Did your problem ever get solved? Would be interesting to know what caused the problem.
 

AidanDanner

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Problem fixed! At long last. Just yesterday. The culprit was the water heater. The hot-water recirc system (pump and pipes) were fine, but the water heater was not -- replacing the heater immediately did the trick. The heater was eleven years old, and our municipal water is very soft, so I hadn't suspected sediment or mineral build-up to be a problem, but at the same time, I never did preventive maintenance on the heater (my bad), so maybe that was indeed the problem. Or something else went wrong with the heater? Anyway, thank you so much for all your help and advice, I much appreciate it!
 

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