Recirc pump at full speed?

[dfuerpo]

I have a hot water recirculation system with a Rinai tankless water heater and a 10 gallon electric buffer heater. About 18 months after all this was installed, the recirculation pump failed. It was a smaller Grundfos model the plumber thought that it had been undersized for the system. He installed a much larger Grundfos pump (model UP26-96BF). I thought that this pump was quite noisy, you could hear it in the upstairs master bath (the pump is in the basement), whereas the older, smaller pump was nearly silent. It started looking at the specs for this pump on the Grundfos website and saw that there were control electronics in the plastic box on the side. Being the curious troublemaker I am, I opened the plastic box to find that there was nothing in there. In other words, this pump has no controller circuit and is simply running full bore! My question is: is this a problem? Is it OK for this fairly large recirc pump to be running a full speed like this? Any help is appreciated.

[havasu]

I believe the original pump was not undersized, but having the system in your basement caused excess strain on it as it pushed the water to the top floor. If the pump shuts down with no water usage, or activates at a specific time, this just meant that the pumps control circuit was bypassed, and is utilizing the TWH's controller. If it fails to shut down at all, it would appear that the pump was directly wired, and I would have the plumber return and installer the controller.

[greenplumber]

Simple solution to this problem is to install an "On-demand" recirc pump. This is the only pump you should be using if you are using a tankless as it will not void the warranty. Secondly, it will only operate when you need hot water, thus it will last you about 15-20 years. Best one is the Metlund D'MAND pump.

[havasu]

I like that "on-demand" system but see two potential downfalls. First, if the TWH has a built in recirculating pump, you would have to gut the old one in order to install the new pump. This would certainly void the TWH warranty.

Another problem is the fact that the switch, either the push button, motion detection or remote control, has to be activated and then wait an amount of time before the pipes get hot enough to use. The concept is great provided you activate the pump, walk away, then utilize the hot water.

As long as your hot water demand is at a scheduled time, I prefer a fool proof timer.

[Reedwalker]

Piping a Rinnai with a 10-12 gallon buffer is in my opinion the very best method with a re-circ. The small tank is economical to run and service. It also relieves the "cold water sandwich". The Grundfos with a built in timer is a reliable and competitively priced unit.

As far as being undersized...........not likely. I service a 3 story building that uses a 1/100 hp pump for its recirc. It worked for 15 years before I changed it to a bigger one.