Are low water cutoffs interchangeable on residential boilers?

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Old 09-23-20, 12:20 PM
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Are low water cutoffs interchangeable on residential boilers?

First post here. I have an old Galaxy boiler (GG225HXPED) which became electrically inactive after running its first time this year. I consulted the manual to see the firing order for the unit and found that the low water cutoff was the first device on the list. It's a Watts OEM 170, a probe-style LWCO. I opened the cover and saw that the exposed part of the probe was rusty and there was a single drop of water hanging from it. Clearly the unit needs to be replaced regardless of whether it was responsible for the shutoff (although I think it is).

I assume that there is no low water situation, because the probe continues to leak slowly. I shut off power to the boiler and placed a piece of plastic below the leak to ensure it dd not soak any electrical parts as seen in photo.

A Watts replacement LWCO is available at about $450 locally. I assume any unit with the same specs would work, TACO or SAFGARD for example. (They're under half the price.) Is that correct?

I know that the probe can be purchased separately, although not sold retail here. To avoid rewiring a new unit, could one just buy a TACO or SAFGARD unit and switch out the probe?

Final question. The wiring diagram shows the two terminals (P1 and P2) that deactivate the burner circuit. If those two terminals were theoretically connected for a few seconds via probe, to determine if the LWCO is the culprit, would there be any downside to that test?

Any insight appreciated.

Watts wiring diagram.


Probe in LWCO
 
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Old 09-23-20, 05:29 PM
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Rather than start shorting out terminals, best to use a voltmeter to troubleshoot in a systematic manner, using a schematic, throughout the control circuit. Where is the 24V being lost? If you think that is beyond your experience level, best to call a tech.
 
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Old 09-24-20, 04:33 AM
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Hi, if the boiler fails to start test across P1 & P 2, you should read 24 VAC if its open.

Geo🇺🇸
 
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Last edited by Shadeladie; 10-02-20 at 07:50 AM.
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Old 09-24-20, 10:48 AM
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Hi all, thank you for responses. The 24v should be lost in the burner control unit, although I am not discounting the possibility that more than one item could be malfunctioning.

Calling a tech in this area is a dangerous proposition, so you want to fully understand a problem if you're going to call one. They tend to Rad Tag older boilers for minor reasons on the possibility they can install a new one. Last one here Red Tagged my boiler because I had an "ambient" CO reading of 6 PPM with the sniffer jammed into the boiler jacket. Three feet from the boiler, CO reading was 1 PPM. You now have to call another HVAC company to put the boiler back in service.

I am going to follow your plan, Geochurchi.
 
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Old 09-24-20, 10:51 AM
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T,
From your pic it looks like your probe/well is leaking. If your LWCO hasn't shorted out you can just replace the probe and use the same LWCO.

There are 2 different probe lengths for that. I believe it would only matter if you are going into a special tee. If going into the boiler directly it probably woundn't make a difference.

Below is the probe number for your control. The SV is the shorter one. To change it out you will have to drain the boiler below the probe point.

https://www.supplyhouse.com/Hydrolev...RoCDOgQAvD_BwE

https://www.supplyhouse.com/Hydrolev...hoCelUQAvD_BwE

If you want to change entire LWCO any brand will do, just make sure you get the right voltage. If you have a gas boiler it is most likely 24V, if you have oil it is 120V. They make both so be sure. If getting just the probe it makes no difference.

Hope this helps a little.
 
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Old 09-24-20, 12:18 PM
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It does help. spott. I was able to get a plumbing store to sell me the identical replacement unit--probe not sold separately -- but the price was only $219. It's a 24 volt unit. The water that dripped into the unit fell only on the little optional alarm device that wasn't activated. The probe goes directly into a tee, just above the boiler. There is a water shutoff valve just above that point, so I will shut it off.

I saw elsewhere in these forums a recommendation to use pipe dope -- not teflon --when installing the probe. Anything else to note, or simply to install with power shut off and not to over tighten?


WATTS LWCO location
 
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Old 09-24-20, 02:21 PM
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It is a matter or preference. Either will work. Just make sure if teflon is used to wind in the right direction when wraping so it doesn't unwind when thereading in the probe.

https://www.google.com/url?sa=t&sour...PM03lpV_flNsFc

If you scroll down to probe data you will see the part number is the same one that was provided earlier. That the sight provided with the probe I believe is the same one that you use for short money. Just for future reference that is a good sight to go to and you can call and they will be happy to help you. Those probes are sold seperately and do wear out. The silver lining here is that you found your part. I believe that is a standard probe for Watts and Hydrolevel or Safeguard.

If it's not too late you can save yourself 150.00 if want and are allowed to return it.
 
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Old 09-24-20, 05:32 PM
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Sorry, I forgot to mention that I'm not located in the U.S., so Supply House won't deliver. Americans can consider themselves lucky with the vast array of products that they can just pick up or order without an HVAC license.

On further examination, it appears that the water drops were falling on an actuator switch with no protective case, and likely shorting it out. The new design fully encases the actuator switch in plastic and locates it off to the side, away from potential falling water droplets. I will fully switch out the entire unit, not just the probe.
 
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Old 09-30-20, 12:12 PM
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For anyone attempting this job or experiencing similar boiler symptoms, I removed the probe and found it completely covered with black deposits. My old probe on the left, new one on the right. I am still not sure how water can pass through/around the device out the front of the probe. I doubt the probe was very conductive with that much of a coating on it.



The probe was in a TEE above the boiler as shown. I turned off the house water supply and the isolator valve above it--but neglected to turn off the return valve, so experienced a face full of water as I attempted to remove it. One great reason to always turn off the electricity supply to the boiler before doing any work.
 
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Old 09-30-20, 02:13 PM
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Congrats, at least you got the job done with minimal damage. Live and learn. Next time you'll be a pro.
 
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Old 09-30-20, 02:24 PM
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I like the McDonnell & Miller RB-24E Guard Dog LWCO. It has a self-cleaning probe. There is a little metal gadget around the end of the probe - the water flowing past the probe causes the gadget to rotate, like a small propeller, and continuously clean the probe. The installation instructions allow pipe dope to be applied sparingly on the male pipe threads, but say that Teflon tape should not be used. The reason is not stated, but perhaps when the Guard Dog is installed or removed (for inspection), Teflon crumbs may be left behind, possibly getting inside the LWCO?

https://s3.amazonaws.com/s3.supplyho..._PROD_FILE.pdf
 

Last edited by gilmorrie; 09-30-20 at 03:46 PM.
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Old 09-30-20, 05:46 PM
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Thanks, Spott!

The McDonnell & Miller Guard Dog sounds like a nice design!
 
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