Hot Water Recirculation pump stops working and appears to overheat

[TaylorN]

I have a Grundfos UP 15-18SU hot water recirculating pump to distribute hot water from my hot water heater throughout our 3600sqft house to showers and faucets. It runs for 12hours each day and has been that way for at least 4 years we have been living here. Just noticed a week ago that it wasn't running but was super hot to the touch (~140-160f I'd guess). I unplugged it and replugged it in but it wasn't running, however it was using 80watts (its rated at 86 watts). I let it cool off for a day before plugging it back in and it does now run when plugging it in, but the temperature of the housing rises from 105f to 145f in like 15mins so I unplug it at that point fearing it may permanently fry the motor. I did remove the "canister" to check the impeller was spinning freely and it spins, but I wouldn't say its super free. It spins a few times then stops. The impeller also has some play in and out which doesn't seem right. When reinstalling I did open the backscrew and let water drain for about 2-3 minutes which is what the manual says to bleed air, but it didn't fix the problem (assuming air was trapped and causing overheating). The pump does seem to be working because it takes about 80 seconds for the water to go from ambient temp to actually coming out of the bleed screw at full hot temp (118f) from the water heater. And without the canister in place water does flow from the input and the output piped. I figure if there was a clog there would be minimal or no flow out of one of the lines?

Note, the pump is plumbed to return water into the bottom "drain" of the hot water heater.

So I could replace just the canister (impeller/rotor) or replace the whole pump. I first chose a used pump off ebay, but it was a bit rusty and ended up actually doing the same thing. It started rising in temp and at one point within the first hour it must have burned up because when I came back to check on it, it was not running, not using any power and the housing was 175f.

Is it coincidental both pumps did pretty much the same thing except one may have actually burned up?

I was thinking about now buying a new one for $300 and hope that my pump just finally dying and the ebay one had a similar issue. But I have some doubts that something may be up with the water heater or lines which is causing the pump to overheat. Maybe the check valve that is installed between the pump and hot water heater drain is jammed and doesn't allow proper flow through back to the hot water heater and the pump is burning up spinning in its own pocket of water? I took apart the pump and water does run a little bit (sometimes more sometimes less) from the output side where the check valve is (photo attached with annotations). I was under the impression that a check valve should not let any water through, but maybe I am wrong. It looks like a spring check valve, but I am not experienced. I should probably replace the pump and the check valve to be safe?

The other thing that bothers me (speaking from inexperience of course) is that the drain from the hot water heater has the spigot on the top of the line (how is that supposed to clear sediment if its not the absolute bottom) and that the drain line goes further downwards towards the recirculation pump. When the recirculation pump is off that looks like an opportunity for the sediment to flow from the bottom of the hot water heater towards the check valve, possible clogging up the check valve and the cooling flow in the rotor area of the recirculation pump. However, when I took a part the recirculation pump and cannister, it didn't look like much sediment was in there, but maybe as soon as I opened the pump the water flushed it all into the bucket and I didn't notice.

Lastly, it looks like the UP 15-18 is no longer made, but a slightly more powerful pump can be used, the UP 15-29 (95watts versus origin 84 watts). I think the 15-18 was rated at 8ft head and the 15-29 is 12 ft heat, whatever that really means ( I get that means it is a little more powerful)

Is there anything else I should check for before just trying the UP 15-29? I'd hate to throw more money away, but am leaning towards just having bad luck and a new motor will be the solution.

I appreciate any thoughts, comments, etc

Thanks!

 

[John Gayewski]

Did you look at the temperature this thing can handle? I would guess over 200degf.

I would leave it alone until it needed replaced, then I would switch to a properly sized taco brand pump as they are better pumps.

 

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[TaylorN]

Did you look at the temperature this thing can handle? I would guess over 200degf.

I would leave it alone until it needed replaced, then I would switch to a properly sized taco brand pump as they are better pumps.

Thanks for the reply!
Yeah, I did notice they can handle in excess of 200F, but figured since the water is ~115F the pump housing should not be getting into the 145F+ range. That screams to me somethings up. Either the motor is shorted (or something like that) and going into thermal shutdown, or the check valve is blocked/clogged and preventing proper flow and the pump is spinning the same water and getting hotter and hotter. Check valve blockage could have damaged the pump, or the pump could have naturally damaged because of time or the rotor is no longer spinning freely from build up or sediment and is generating a lot of friction/heat.

 

[John Gayewski]

Thanks for the reply!
Yeah, I did notice they can handle in excess of 200F, but figured since the water is ~115F the pump housing should not be getting into the 145F+ range. That screams to me somethings up. Either the motor is shorted (or something like that) and going into thermal shutdown, or the check valve is blocked/clogged and preventing proper flow and the pump is spinning the same water and getting hotter and hotter. Check valve blockage could have damaged the pump, or the pump could have naturally damaged because of time or the rotor is no longer spinning freely from build up or sediment and is generating a lot of friction/heat.

No. They get hot. If your pipes are warming up then it's pumping.

The fact that it stopped probably means it's getting toward the end of its life. But like I said run it until it's done and get a new one. Preferably a taco cartridge circulator.

 

[TaylorN]

No. They get hot. If your pipes are warming up then it's pumping.

The fact that it stopped probably means it's getting toward the end of its life. But like I said run it until it's done and get a new one. Preferably a taco cartridge circulator.

Ok. Time to get a new one then because the pump will stop pumping after running for about 30mins, but still draw power. And if I leave it like that, it will never resume pumping until I unplug it and let it cool off.

Any reason to get a taco cartridge recirculator vs the taco smart plus recirculator? I can replicate the on/off interval timer of the smartPlus series with the smart outlet I am already using to turn on/off the pump at night. So I guess the regular cartridge one without the bells/whistles should be fine.

What specific taco recirc pump would replace the Grundfos UP15-18? I can't figure out how much power/head is needed. I'm just not familiar enough with that. We have a 2 story house for whatever that is worth.

And based on the Taco install instructions I would need to modify the plumbing to incorporate more drain valves to purge air with the Taco, where as I think the screw on the back of the grundfos allows me to purge air from there?

Thanks!

 

[John Gayewski]

How many linear feet of piping from the water heater to the farthest fixture and back again? That'll tell you how many feet of head the pump needs to overcome at speed.

You should be able to bleed air from the water heater drain, assuming your piping was set up to do so. If not then a companion flange gets broke to bleed air or any number of other ways.

The reason I like the cartridge circulator is 10 or more (likley way more) years from now when this happens again you can just pull the cartridge out and replace it. The power can be done any number of ways with a timer aqua stat or plain old switch of you like.

 

[TaylorN]

How many linear feet of piping from the water heater to the farthest fixture and back again? That'll tell you how many feet of head the pump needs to overcome at speed.

You should be able to bleed air from the water heater drain, assuming your piping was set up to do so. If not then a companion flange gets broke to bleed air or any number of other ways.

The reason I like the cartridge circulator is 10 or more (likley way more) years from now when this happens again you can just pull the cartridge out and replace it. The power can be done any number of ways with a timer aqua stat or plain old switch of you like.

ok. I'd guess 100-150ft.

Couldn't I also replace the cartridge of the grundfos similar to the taco? do you just find the taco to be more reliable, or do they all pretty much last about 10 years?

 

[John Gayewski]

ok. I'd guess 100-150ft.

Couldn't I also replace the cartridge of the grundfos similar to the taco? do you just find the taco to be more reliable, or do they all pretty much last about 10 years?

I'm not familiar with the grundfos, but your description sounds like you should be able to, but I thought you researched it and said they didn't make it anymore. Yes taco makes a better pump they last longer.

 

[TaylorN]

I'm not familiar with the grundfos, but your description sounds like you should be able to, but I thought you researched it and said they didn't make it anymore. Yes taco makes a better pump they last longer.

Grundfos makes a different model (UP15-29) that is supposed to be a direct replacement size wise, but is a little more powerful (+10watts)

 

[John Gayewski]

Whatever pump you get should do 3 to 4gpm at 9ft.of head.