The pump is either installed in reverse, you are missing the ever important check valve (if you dont have the circ with one built in). But I am assuming it worked for awhile? so see below-

If it is the comfort pump system with a plastic manifold installed under a sink with the supply lines, and the pump on the hot water outlet of the water heater the thermostatic bypass manifold has most likey failed open. Common with sediment getting to manifold unit or hard water installs. If you have this type of system, you should have been warned about well water, hard water or sediment in water causing this problem.

Understand, right now the problem is not mine because it belongs to her. However, in time it will become my problem. The water there certainly is hard (I don't know how many grains per gallon).

If I could find a competent plumber and either persuade her to have it looked at OR manage to sneak in a plumber, sounds like it could be fixed. I just know it's not right and I am certain it was installed incorrectly. By the way, when I was just there, I could take an entire shower using the "cold" water (which is plenty warm), whicn means I would have had to run the shower for at least 10 minutes before getting cold water out of the cold water side.

The hot water can't be doing the ice maker and cold water system in the refrigertor/freezer any good, right?

Depending on the model of the recirc pump, your system is probably working "as designed". Most residential technology comes from Commercial technology, meaning manufacturers and contractors who work in both fields transfer the technology. One technology is the recirc pump. In commercial construction you have a recirc pump and a separate recirc line with a check valve and balancing valve. This type of system could easily cost $500. So some manufacturer got a cost saving idea, he could provide a recirc pump in a residential application and save the cost of the recirc line by utilizing the cold water line to recirc water back to the water heater. You will have hot water all the time, but you will also have warm water in the cold water supply. Now there are several pumps out for sale that operate this way, the only proper way is run a separate recirc line & insulate the pipes. The pump runs off an aquastat, a check valve makes sure the flow is one way.

Another technology is called heat tracing. An electric heating cable with a specified temperature (Say 110 degrees) is installed on the hot water main to maintain the specified temperature in the pipe. This system is less costly than a recirc pump, and less maintenance. The product is made by Raychem and is used in the commercial field, but could easily be used in residential applications.

Take Care,

Dan Martyn

The problem is inherent with Grundfos circulators which use the black comfort valves under the sinks. Those valves open and close depending on the water temp in the valve. For the valve to close 95 degree water must be maintained at the valve and this is accomplish by the pump running non-stop when the timer is in an ON state. This also causes a near continuous flow of 93 degree water entering into the cold water line slowly heating up the cold line as it makes its way back to the water heater.

To avoid this problem don't use thermostatic valve circulators. Instead use one with more up-to-date technology by selecting one with a solenoid valve instead or at a minimum one which pumps only wwhen the temperature drops (cyclic operated).

Is a constantly running Grundfos hot water recirculation system incompatible with White-Rodgers 37C73U-XXX series natural gas control valves? I had a new American Standard 40-gallon ultra low NOX natural gas water heater installed in November 2019. There was an existing Grundfos hot water recirculation pump on the 16-year old water heater that was moved to the new water heater. This was a preventative replacement, the existing water heater installed in 2003 was still working okay. The Grundfos bridge valve, also installed in 2003 under the sink in the most distant bathroom, was replaced a month later, since sometimes would only have warm water, so thought the bridge valve might have worn out. The timer clock on Grundfos pump had failed circa 2016, so the Grundfos had been switched from "timer" to "on," and allowed to run continuously. Had repeated episodes of warm water only with the new American Standard water heater, so in August 2021 plumber installed a replacement gas heater valve, as a warranty replacement (6-year warranty on American Standard water heater). Everything was fine for first six months or so, then again started getting unreliable hot water. Plumber couldn't find any visible problem, so had the now 18-year old Grundfos pump with its 3-year old bridge valve replaced, but did not fix problem. So plumber then did a second warranty replacement of the White-Rodgers gas control valve. When he removed the first replacement gas valve, which had only been in use for 11 months, the shank was coated with black corrosion. Plumber believes that the constantly running Grundfos system contributed to the problem. Have changed operation of my new Grundfos pump from "on" to "timer," for just three hours per day, from 6 AM to 9 AM. So is this a problem with the White-Rodgers gas control valve, the copper shank doesn't like a constantly running hot water recirculation system?