Grundfos recirculating pump caught fire

noblehouseJune 11, 2014

I have a Grundfos Comfort Series hot water recirculating pump installed on the water heater. It was here when we bought the house so I don't know how old it is. A few days ago we noticed we weren't getting hot water, and I went out to take a look. The timer seemed to be set correctly and it was plugged in, but I didn't have time to investigate further. A few days later I went out to look again, and saw that at some point it caught fire. The timer side of the pump was completely burned away. I don't know when this happened, but I'm lucky the house didn't catch fire.
Until this happened we were pleased with the system--there's a drought here in California and we were wasting a lot of water waiting for the hot water, so I'd like to get another. But now I'm hesitant -- what would cause this to happen? Is this a known problem with Grundfos pumps?

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Grundfos is the most popular equipment used in commercial systems. It was just time for the pump to go. I would reccomend properly fuseing the new pump,the breaker should have tripped before that much damage.

    Bookmark   June 11, 2014 at 2:39PM
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I agree that Grundfos is a major supplier of commercial equipment.
This particular pump is residential grade.

I don't agree "that it was just time for the pump to go". The pump didn't go, the timer did.

That said, it shouldn't have burned up. I would let Grundfos know about it. They may want it to see why that happened. They might even replace it.

I also disagree that the breaker should have caught this - this was an arcing problem, not an overcurrent problem. It was caused by a loose connection or contact.

    Bookmark   June 12, 2014 at 9:18AM
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"The pump didn't go, the timer did. It was caused by a loose connection or contact."

That's an interesting and all inclusive observation jake. I am a student of electro-mechanical systems and never tire of learning when opertunity presents itself. What happed with the timer, Did it fail to come on when it should,fail to go off when it should or begain continusly arcing on and off causeing the motor windings or something else to flame out? I am also bumfuzzled over why the current would not greatly increase with that much heat being created. If the pump and timer motors normaly consume 4.8 amps (just for demonstration) and have a 8 amp reset or fuse,would there not have been enough overcurrent to shut down before things reached the point of meltdown. I'm also not understanding why a high resistance caused by loose connection would not result in increased current draw. Hopful this is still on topic because I realy do want answers so as to better understand how all this came about and how it could have been prevented. IMO,the expense and aggervation of this problem pales in light of the structure fire that might have resulted.

    Bookmark   June 12, 2014 at 5:34PM
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Why would you assume that the current would increase?

The motor appears to be fine. If the motor had overheated, and the insulation on the windings had broken down then the current would have increased. There's usually a thermal overload that prevents that type of failure from progressing.

This appears to be the timer - not the motor. My guess is that the contacts on the timer began to arc either when they were opening or closing. Once the contacts start to arc, the carbon and such increases the resistance of the contacts and they heat up - it goes downhill pretty quickly.

An arcing condition can cause fires - because the arc is quite hot and because the connection resistance increases. Such faults are not detected by over-current devices until it fails to such an extent that it shorts out.

There are arc fault protection devices that can detect and shut down circuits. See below

Here is a link that might be useful: AFCI

    Bookmark   June 12, 2014 at 10:55PM
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"I'm also not understanding why a high resistance caused by loose connection would not result in increased current draw."

Are you familiar with Ohm's Law? As resistance goes up, current goes down - assuming that voltage remains the same. A high resistance connection would result in lower current.

What's more, the lowest amperage breaker on residential wiring is 15 amps and 20 amps isn't uncommon. The pump motor draws 0.23 amps when running. A 15 amp breaker isn't going to see a problem here until the unit basically shorts out.

    Bookmark   June 13, 2014 at 10:41AM
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