aquastat problem?

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  #1  
Old 10-01-14, 02:28 PM
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aquastat problem?

I have a gas-fired boiler, two zone hydronic system with a single circulator. Honeywell triple aquastat L8024E. System appeared to have tankless hot water at one time which is now capped off. The problem is that the circulator started humming with no call for heat from the thermostat. Humming only stopped when power was turned off to the system. When there is a call for heat, the relay closes but water doesn't appear to circulate. When the relay closes I measure 120VAC going to the pump, but with the relay open, I still measure about 40 VAC. Is there a problem with the aquastat?
 
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Old 10-01-14, 02:59 PM
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Is there a problem with the aquastat?
Maybe...

It sounds as if there may be a problem with the circulator as well. If you have 120VAC to the pump and it doesn't run, that would seem to be a problem with the pump.

Sometimes a meter will read random low voltage when the relay is open... that MIGHT be what you are seeing with the 40 VAC reading, but I can't tell you that from here.

The fact that the pump is 'humming' with the relay open suggests that there may also be a problem with the aquastat.

What voltage do you read from GROUND ( chassis of aquastat for example ) to each of the following ?

BE CAREFUL! 120 VAC IS PRESENT! YOU CAN BE KILLED!

GROUND to L1 = ?

GROUND to L2 = ?

GROUND to C1 with pump OFF = ? with pump ON = ?

GROUND to C2 with pump OFF = ? with pump ON = ?

I'm checking to make sure the incoming power is the correct 'polarity' ... yes, I know AC doesn't have a polarity, I want to make sure that the L1 and L2 are correct... L1 = HOT , L2 = NEUTRAL

What make and model is the pump?
 
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Old 10-01-14, 04:00 PM
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Thanks for the quick reply.
L1 to ground 0v (white wire )
L2 to ground 120v (black wire)
C1 to ground 19v circ off; 0v circ on (black wire)
C2 to ground 120v circ off; 120v circ. on (white wire)

I've already taken the pump out so the readings with "circulator on" I made by manually closing the relay contact - is that ok?

Looks like the L1 and L2 are reversed?

Pump is Taco 007-F4

Thanks
 
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Old 10-01-14, 04:32 PM
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readings with "circulator on" I made by manually closing the relay contact - is that ok?
Yes, should be...

Looks like the L1 and L2 are reversed?
Yes, it sure does!

L1 should absolutely be the black HOT, and L2 the white NEUTRAL.

So reverse those right off the bat for starters.

Leave the C1 black and C2 white, that is correct and once the L1 and L2 are reversed, the C1 and C2 will also be correct.

This could possible account for some of the stray voltage readings that you are seeing.

So recheck and see what you get after L1 and L2 are corrected.
 
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Old 10-01-14, 04:43 PM
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By the way, it sounds to me as if the aquastat is OK.....................
 
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Old 10-01-14, 04:48 PM
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I've already taken the pump out
I take it that the pump rotor turns freely by hand?

Here is another test: measure the resistance from either side of the windings and to the motor stator, while the motor is electrically disconnected from the line.
 
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Old 10-01-14, 06:04 PM
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Here is another test: measure the resistance from either side of the windings and to the motor stator, while the motor is electrically disconnected from the line.
What should it measure?.............................
 
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Old 10-01-14, 06:05 PM
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OK, I reversed L1 and L2. Ground to L1 is now 120v and to L2 is 0v
Ground to C1 is 1.6v with pump off and 120v with pump on
Ground to C2 is 0v for both pump on and off.
 
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Old 10-01-14, 06:09 PM
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The rotor does turn freely by hand. Which leads to I measure the resistance?
 
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Old 10-01-14, 06:10 PM
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What should it measure?
Resistance, ohms..........................
 
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Old 10-01-14, 06:11 PM
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Resistance, ohms..........................
How many?..................................
 
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Old 10-01-14, 06:12 PM
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OK, I reversed L1 and L2. Ground to L1 is now 120v and to L2 is 0v
Ground to C1 is 1.6v with pump off and 120v with pump on
Ground to C2 is 0v for both pump on and off.
Sounds fine now Frank... and MUCH SAFER TOO!
 
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Old 10-01-14, 06:13 PM
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Which leads to I measure the resistance?
Either................................
 
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Old 10-01-14, 06:18 PM
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Also, when the pump was buzzing, the motor got very hot
 
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Old 10-01-14, 06:24 PM
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Measures 8 Mohms, If I'm doing it right (either lead to center)
 
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Old 10-01-14, 06:24 PM
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Also, when the pump was buzzing, the motor got very hot
And you're certain that there was no call for heat at that time?

Has any work been done on the system that might have caused L1 and L2 to be reversed, or has it always been that way to your knowledge?
 
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Old 10-01-14, 06:27 PM
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Great. I'll put in the new pump and see if it works. The aquastat has been wired that way for as long as I know, at least 15 years. Thanks very much for your help.
 
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Old 10-01-14, 06:31 PM
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No call for heat. I even disconnected the thermostats.

No work was done on the system since the pump was replaced about 15 years ago except for purging the air last time about a year ago.
 
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Old 10-01-14, 06:48 PM
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Well, the only thing that I can figure is that there was an internal short somehow inside the motor.

Because the HOT and NEUTRAL were reversed, it means that the HOT was always connected to the pump. A short inside the pump could have caused it to be powered by passing the current to ground.

That's the only thing I can think of...

But your resistance readings seem to imply that is not the case.

Is the wire from the aquastat to the pump the metal sheathed stuff? (it should be)

Is it in good condition? Is it possible that the metal sheath cut into one of the wire insulation at the end?

Are you familiar with 'anti-short bushings' aka 'redheads' that are used on metal sheathed cable?


image courtesy bwmfg.com


image courtesy popularmechanics.com

You might want to very carefully examine that wire... and replace it if it looks shabby.
 
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Old 10-01-14, 07:12 PM
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The wire from the aquastat to the pump is metal sheathed. It looks like it's in fairly good condition but it does not have the red-head. I don't see any breaks in the insulation but will examine more carefully.

I'll try with the new pump. A question about installing the pump: the old one had the red, full-flange gaskets, even though it has the grooves for the circular gasket. The old flanges aren't exactly smooth but I'd like to use them since it looks difficult to get in to replace them. WOuld the red full gaskets work better than the circular ones that come with the pump?
 
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Old 10-01-14, 07:31 PM
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Yeah, changing flanges is a PITA.

I think either type gasket will work fine, use what you like best... maybe spread a thin layer of that RTV form-a-gasket stuff before installing.

Tighten the two sides of the flange evenly... so the flange face is parallel with the pump flange.
 
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