Testing whether a pump is running

RayWohlfarth

Today is the second time this happened and I wanted your opinion. We had a grundfoss and a Honeywell circulator and when I held my phone using the danfoss magnet tool, it showed the pump was energized and spinning when it wasn't. I even used the Grundfoss magnetic tool with the same results. In both instances the pump was not running. The motor was blazing hot. Just curious if you have seen this or is it just a Pittsburgh PA things?

GGross

Those magnet tools don't actually tell you the pump is spinning, just that there is power there. They are misleading to say the least.

Alan (California Radiant) Forbes

Energy is being delivered to the pump which is what the Danfoss tool picks up and identifies. In your case, that electrical energy is heating the pump instead of turning the impeller.

You can call it, "The case of the overheating pump.".

ScottSecor

Trying to learn here, if there was significant gravity flow could that spin the impeller?  Would that "fool" your Danfoss or Grundfoss tool?

Intplm.

ScottSecor said:

Trying to learn here, if there was significant gravity flow could that spin the impeller?  Would that "fool" your Danfoss or Grundfoss tool?

It can but probably not under all circumstances.
Not being able to see a shaft move on a circulator brings this confusing issue up now and again.
It's probably the only thing I dont like about the wet rotor circulator design. You can not physically see the shaft turning like you can on the older three-piece circulators.

EBEBRATT-Ed

Is ghost flow from another zone turning the pump motor into a generator??

Can't you just put an amprobe on the pump to see if it is running?

Alan (California Radiant) Forbes

@EBEBRATT-Ed said:

Can't you just put an amprobe on the pump to see if it is running?

If the impeller is stuck, I'll bet you're drawing >2amps.

ScottSecor

I an very much aware that many installers do not install an isolation valve on the pump outlet.   However,  if there is an isolation valve on the outlet,  simply throttle it down and you'll hear the water flow change.  

EdTheHeaterMan

I used this a lot. I keep it in a bag that my old wet combustion kit is in. When I pull out that bag, and start pumping the Carbon Dioxide bottle with flue gas, taking the temperature and listening to the pump motor with the stethoscope, customers like to joke about me being a heater doctor. "That is so I can charge you Doctor rates," Then the joke is on them Ha Ha Ha.

PC7060

Agree with Ed but I don’t have his fancy tool, I use a screw driver as my stethoscope.

hot_rod

if you spin an unpowered Alpha the lights blink

RayWohlfarth

Thanks all. I tried the screwdriver stethoscope like @PC7060 and heard pump movement but it was the pump downstream. I finally went by the delta t and it was zero. @Alan (California Radiant) Forbes this will be a new case LOL
Just weird cause I have used my magnet tool on circulators and solenoid valves. I guess all it does is verify voltage is applied. I was told when it spins it tells you the pump is moving. Can't believe a sales person fibbed

hot_rod

Makes you wonder how many pumps  have been been wrongfully diagnosed and replaced based on that tool?
I don’t think it works on all pumps, not ECMs for sure

its more of a power available indicator😗

pecmsg

Like a no contact voltage pencils. Not to be trusted!

JUGHNE

With the stethoscope method, as you listen, cycle the power to that pump to hear a change.

If running at all you will hear it.

RayWohlfarth

@hot_rod I remember the grundfoss rep telling me it wouldshow the rotation. Guess he was mis informed too. @pecmsg I guess that all I can use it for is to check if voltage is present
@JUGHNE Im going to get my old stethoscope and bring it back
Thank you gentlemen

pecmsg

RayWohlfarth said:

@hot_rod I remember the grundfoss rep telling me it wouldshow the rotation. Guess he was mis informed too. @pecmsg I guess that all I can use it for is to check if voltage is present
@JUGHNE Im going to get my old stethoscope and bring it back
Thank you gentlemen

Id stick with the proper tools.....................Volt Meter.

hot_rod

It might show rotation, it might not.

So not a very reliable tool to own

Dave H_2

The Danfoss app and the keychain spinny thingamijig all they detect is a magnetic field. A motor that is powered will create a magnetic field therefore making the cartridge spin. If the cartridge doesn't spin, the magnetic field is still going to be created.
It sounds like what you have is a seized impeller, the first thing I would do is tap the circulator (lightly) to maybe "break free" what's keeping it place. Most likely at this time of the year, the volute casting may have rusted over the summer from no use and the tolerance between the impeller and the cast iron is around a 32nd of an inch.
If this continues to be an issue from season to season, you may need to either chemically or mechanically treat the boiler water.

Jamie Hall

Let us suppose for the moment that the gadget can, in fact, detect a rotating magnetic field (I've never used one so I really can't say what it does do!). But... a rotating magnetic field, which is what causes the motor armature to turn assuming all is well, does not mean that the motor armature is, in fact turning. It is perfectly possible for the magnetic field to spin quite merrily, and the armature to be seized. In fact, on a device with sleeve bearings and close tolerances which has been sitting for a while it's not really all that surprising. It can take a surprising amount of torque to get a seized armature to behave. The real question then is once you do get it to run, will it be able to start the next time it is stopped? And the answer to that is... a resounding maybe. Much better to take the thing apart, clean up any corroded or crusty bearings found, and relubricate -- and hope.

RayWohlfarth

Well we found the issue with the pump. the impeller broke and bound inside the volute. The new one is working great so @daveh_2 was right

JOutterbridge

Great follow up 👍 Just shows that tools are tools and don't always give the info you need. (Voltage pens included) I usually test amps with a meter to find a seized pump. And then flow test/deadhead test. And temp/pressure check if possible. Whatever it takes to reach a definitive logical answer most efficiently:)

RayWohlfarth

Thanks @JOutterbridge Good point