Is My Underfloor Hydronic Pump Undersized?

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Passenger

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I live in a two storey, two bedroom, two bathroom condo with hydronic heating for both floors. Heating is divided into four loops, each 300 feet long, 3/8" Pex. In case it makes any difference, I have a Bradford White combined potable/underfloor heating water heater rated at 65,000 BTU.

The recirculation pump currently installed in my system is a Grundfos UPS15-55SFC. According to Grundfos, this pump rated as follows:
Replacement Pump
Model: Grundfos UPS15-55SFC
P/N: 59896773P1
Rated Flow: 11.1 US gpm
Max Flow: 25.1 US gpm
Rated Head: 8.042 ft
Max Head: 18.05 ft

The pump originally installed in my system was a Grundfos model UP 26-64 F which, according to Grundfos, is rated as follows:
Original Pump
Model: Grundfos UP 26-64 F
P/N: 52722330
Rated Flow: 14.9 US gpm
Max Flow: 32.1 US gpm
Rated Head: 14.49 ft
Max Head: 24.61 ft

The replacement pump is about 6 months old and has not been in use much. When running, it will occasionally make noise. The pump housing is very hot to the touch, much hotter than the recirculating hot water. The replacement pump is the second such model UPS15-55SFC which has been installed in my system. The first UPS15-55SFC also started making noise and was relaced after about 6 months in use.

Given this information, is the UPS15-55SFC undersized for my system? Or is something else causing the pump to quickly fail?
 

WalnutContractors

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I live in a two storey, two bedroom, two bathroom condo with hydronic heating for both floors. Heating is divided into four loops, each 300 feet long, 3/8" Pex. In case it makes any difference, I have a Bradford White combined potable/underfloor heating water heater rated at 65,000 BTU.

The recirculation pump currently installed in my system is a Grundfos UPS15-55SFC. According to Grundfos, this pump rated as follows:
Replacement Pump
Model: Grundfos UPS15-55SFC
P/N: 59896773P1
Rated Flow: 11.1 US gpm
Max Flow: 25.1 US gpm
Rated Head: 8.042 ft
Max Head: 18.05 ft

The pump originally installed in my system was a Grundfos model UP 26-64 F which, according to Grundfos, is rated as follows:
Original Pump
Model: Grundfos UP 26-64 F
P/N: 52722330
Rated Flow: 14.9 US gpm
Max Flow: 32.1 US gpm
Rated Head: 14.49 ft
Max Head: 24.61 ft

The replacement pump is about 6 months old and has not been in use much. When running, it will occasionally make noise. The pump housing is very hot to the touch, much hotter than the recirculating hot water. The replacement pump is the second such model UPS15-55SFC which has been installed in my system. The first UPS15-55SFC also started making noise and was relaced after about 6 months in use.

Given this information, is the UPS15-55SFC undersized for my system? Or is something else causing the pump to quickly fail?

I've got the same circulator. The alpha typically shows the gpm and the watts that are currently in use - what does yours show? Do you set yours to auto?

I am running my system off a low boy bradford white. I have 7 zones in 5/8 pap with 3 floors and a crawl ( pump is at the crawl level ). My zones range from 204ft to 278ft. My pump is quiet and about the same temperature as the return water since I am pumping toward the low boy but away from my expansion tank. Your 3/8 pipe will have more impedance to flow than my 5/8 but I'd expect your pump to be the right size.
 

WorthFlorida

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I'm in no way acknowledgeable with hydronic systems but the first thought is the system might be getting air bound, thus not enough water is circulating to cool the motor down. Perhaps it's the reason for the housing is getting very hot? With two motors failing the same way, making noise indicates an installation problem. But I could be wrong. Please post a picture of the manifold and pump. Where is the air vent installed?

See page four of the installation manual, motor orientation and an air vent is used. https://s3.amazonaws.com/s3.supplyhouse.com/product_files/59896773-install.pdf
 
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