Seeking advice on issue with hot water recirculation system

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djwbd92

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My home has a hot water recirculation pump installed that doesn’t use a dedicated return line (The Grundfos Comfort System). This setup uses a thermostatic bypass valve at the far end of the loop in the 2nd floor master bathroom, so that the cooled water in the hot water line is pushed back to the water heater when the pump is running. Once the water in the hot water line gets hot, the bypass valve closes to prevent the hot water from continuing to flow into the cold water line. I’ve had this pump installed for 6-7 years, and during much of that time it’s worked very well. At worst the cold water might get slightly warm once the pump had been running for a while.

Unfortunately, sometime in the last 1+ years, something has changed such that the cold water actually becomes uncomfortably, if not dangerously, hot if the pump has been running for 10 or more minutes. I have replaced the thermostatic valve, and tested that the new valve is properly shutting off once the water in the hot water line gets hot, so I’m fairly certain that is not the problem. Could the hot water be bleeding into the cold water somewhere else in our plumbing system, like in one of the shower cartridges or shower valves?

I had a plumber come by to look at this, and despite my telling him that the bypass valve was new and showing him how the water being pushed up the hot water line stopped once it reached temperature and the valve closed, he insisted that the bypass valve was the problem and told me we should get a dedicated return line installed, to the tune of $3800, since that is the “right” way to do it. He insisted they could install the return line without punching holes in my walls by installing it from the crawlspace, which I’m not even sure if that makes sense.

I’d greatly appreciate any thoughts on other explanations for why the current recirculation setup is causing our cold water to become so hot. Also, I realize that a dedicated return line would work better in that it would avoid causing any temperature changes to the cold water, but is it really possible to install a dedicated return line in an existing house without opening up the walls and generally making a mess?
 
Turn off the cold water to the water heater.

Go to a hot water faucet and turn it on......the pressure should bleed down and the water should completely stop running.

If it doesn’t you have a cross connection between hot and cold.

If you think the bypass valve could be the cause, turn the cold water valve off at the bypass under the sink. If it’s the bypass, the water should stop now.

This is assuming all your stop valves operate 100%.
 
It’s possible to do a return without tearing up a house but that depends on the house.

I wouldn’t spend 4K on a return when my bypass and pump worked great for years.

If you had a cross connection other than the bypass valve what the plumber is suggesting wouldn’t correct your core problem.
 
My home has a hot water recirculation pump installed that doesn’t use a dedicated return line (The Grundfos Comfort System). This setup uses a thermostatic bypass valve at the far end of the loop in the 2nd floor master bathroom, so that the cooled water in the hot water line is pushed back to the water heater when the pump is running. Once the water in the hot water line gets hot, the bypass valve closes to prevent the hot water from continuing to flow into the cold water line. I’ve had this pump installed for 6-7 years, and during much of that time it’s worked very well. At worst the cold water might get slightly warm once the pump had been running for a while.

Unfortunately, sometime in the last 1+ years, something has changed such that the cold water actually becomes uncomfortably, if not dangerously, hot if the pump has been running for 10 or more minutes. I have replaced the thermostatic valve, and tested that the new valve is properly shutting off once the water in the hot water line gets hot, so I’m fairly certain that is not the problem. Could the hot water be bleeding into the cold water somewhere else in our plumbing system, like in one of the shower cartridges or shower valves?

I had a plumber come by to look at this, and despite my telling him that the bypass valve was new and showing him how the water being pushed up the hot water line stopped once it reached temperature and the valve closed, he insisted that the bypass valve was the problem and told me we should get a dedicated return line installed, to the tune of $3800, since that is the “right” way to do it. He insisted they could install the return line without punching holes in my walls by installing it from the crawlspace, which I’m not even sure if that makes sense.

I’d greatly appreciate any thoughts on other explanations for why the current recirculation setup is causing our cold water to become so hot. Also, I realize that a dedicated return line would work better in that it would avoid causing any temperature changes to the cold water, but is it really possible to install a dedicated return line in an existing house without opening up the walls and generally making a mess?
I have seen a cross-connection happen from a clothes washer that both hot and cold are left on.
 
Considering your system is a band aid after thought system I would install a dedicated return. It's likley possible and if the plumber thinks he can do it I don't know why you think he can't, unless there's something you haven't mentioned.
 
Considering your system is a band aid after thought system I would install a dedicated return. It's likley possible and if the plumber thinks he can do it I don't know why you think he can't, unless there's something you haven't mentioned.

4k on a return line is a little pricey. 🤣
 
Considering your system is a band aid after thought system I would install a dedicated return. It's likely possible and if the plumber thinks he can do it I don't know why you think he can't, unless there's something you haven't mentioned.

It's not that I think he can't, I'm just unsure how doable it is without having to open up walls.
 
Turn off the cold water to the water heater.

Go to a hot water faucet and turn it on......the pressure should bleed down and the water should completely stop running.

If it doesn’t you have a cross connection between hot and cold.

If you think the bypass valve could be the cause, turn the cold water valve off at the bypass under the sink. If it’s the bypass, the water should stop now.

This is assuming all your stop valves operate 100%.

Should I do this while the pump is running, or turned off?

I've already done what you suggest with the cold water valve at the bypass, with the pump running, and the cold water faucet stops flowing once the water in the hot water line gets hot enough to cause the bypass valve to close. I took that as evidence that the bypass valve is working as designed.
 
All the bypasses I have installed have a check valve and are not thermostatically operated. Can you post a link or part number to your thermostatic bypass?
 
The person wrote: "I’ve had this pump installed for 6-7 years, and during much of that time it’s worked very well."
Something has changed on his system and it is imperative to find out what has changed. Putting in dedicated return line at this time does not correct the problem and is a waste of money.
 
People like those bypass systems. I have a lot of customers that have them.

A couple of my customers have bought them as gifts for their adult kids and had me install it, they all love it and it costs less $500 installed. That’s parts and labor.

Success is hard to argue with.
 
My last 3 houses have had the Grundfos "instant" hot water systems. I spend ~ $250 and install them in about 15 minutes. I love them and sure is alot cheaper than a dedicated return line. The only drawback is my cold water is luke warm for the first 10 seconds, but I don't mind.
 
If your installing yourself a dedicated return should be about the same price. Pump, check, pipe, fittings.

If its your only practical option then the bypass would be fine. It's just an inferior system.
 

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