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Need help with indirect DHW

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I need some help diagnosing a problem with a Bradford White SW280L indirect water heater.

I noticed that the water heater was calling for heat hours after my wife and I took our morning showers. I contacted Bradford White who thought it was a faulty aquastat, covered under warranty. I got a new aquastat, and when replacing it, noticed that there was no thermal grease in the well. Bradford White agreed that was an error in manufacturing. I got some grease, Honeywell 107408, and injected it into the well, and installed the new aquastat.

I still see significant delay in the water heater turning on. I ran a test today to see what was happening.

I checked the water temperature by running the water and checking the temperature at the tap. It was 154 degrees. I ran the hot water until the hot water ran out, and watched to see when the water heater called for heat. I got the water temperature down to 65 degrees, and the water heater still did not turn on. One hour and 40 minutes later, the water heater turned on. It turned off one hour later, and the water temp was 150 degrees.

The aquastat is set to 115 degrees.

This doesn't seem normal, but I can't tell what is wrong.

I checked the original aquastat with a pot of water, some ice and an ohmmeter. It opened and closed immediately with a hysteresis of around 10 degrees.

Bradford White mentioned that it might be something they called "stacking" but I didn't understand what that meant.

Can any of you experts help explain what I'm seeing, and suggest tests to try?

Thanks in advance.

~~Andy
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Comments

  • HVACNUT
    HVACNUT Member Posts: 5,865
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    I never heard of that model Honeywell aquastat or controller.
    Pic?
    Where is the wire from the Honeywell going? Presumably a relay. Is it possible there's an intermittent problem with the relay?
  • hot_rod
    hot_rod Member Posts: 22,268
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    Does the aquastat turn on a pump,or zone valve?
    If it triggers a zone valve, the end switch could be acting up and not calling the boiler on.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterManSuperTech
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
    edited December 2022
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    HVACNUT said:

    I never heard of that model Honeywell aquastat or controller.
    Pic?
    Where is the wire from the Honeywell going? Presumably a relay. Is it possible there's an intermittent problem with the relay?

    It is the "thermal grease" the OP is referring to. Heat conductive compound. https://www.amazon.com/Honeywell-107408-Heat-Conductive/dp/B0006UPMZM

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    @EdTheHeaterMan the 107408 is heat conducting compound.

    @andycoop

    10 deg diff is ok i guess I would prefer 5. What does the aqua stat power up as others have mentioned? zone valve a relay?

    I would disconnect the aqua stat wire with the power off. Then turn the power on and carefully jump the wires together and see what happens. If the aqua stat opens a zone valve, then the zone valve should open and its end switch should fire the boiler within a minute or so unless the boiler is off on limit.

    If the aqustat starts a circulator its possible the circ is defective and the tank is only getting heated when your heating system calls for heat.

    That might describe the erratic operation.

    You might also call Bradford White and ask them what a defective dip tube would do
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
    edited December 2022
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    Water heater stacking happens when the thermostat turns on the heat source, maybe near the bottom of the tank, while there is still hot water at the top of the tank. The cold water enters the bottom and the temperature sensor of the thermostat is close to the cold water. If you use about 5 gallons of hot water, then the bottom 5 gallons turn on the heat source. In a few minutes the thermostat is satisfied. then 15 minutes later you use 5 gallons again. The water at the top is still hot but the cold water at the bottom activates the thermostat again. do this several more times and the water at the top of the tank is well above the thermostat setting. the water in the middle of the tank is a little hotter than the thermostat setting and the water at the bottom of the heater is at the thermostat setting once the thermostat is satisfied.

    There are different temperatures stacked at different levels of the tank. here is a source to look at concerning stacking. http://waterheatertimer.org/Stacking.html

    Your description does not sound like stacking. Since I'm not familiar with the sensor well location of the Bradford indirect, I can only speculate, but there is the possibility that your well has some kind of insulating build up on the water side of the sensing well. What if the packing styrofoam is still on there inside the tank. Stranger things have happened

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,112
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    Its similar to the Thermocline of a lake. Mad 🐕 Dog
    SuperTech
  • andycoop
    andycoop Member Posts: 7
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    First, thanks to all for the informative comments. I really appreciate the help.

    The aquastat controls a circulator pump connected through a Taco 502 2-zone priority relay. The water heater is the priority zone, so when it calls for heat, the other zones are turned off. I am monitoring the status by looking at the LEDs on the Taco box. As far as I can tell, when the LED for the water heater is lit, the system works properly. The circulator is energized, and the boiler fires if necessary, and the water in the water heater rises in temperature.

    What I'm seeing is when the water in the water heater is cold, the LED on the priority relay doesn't turn on until much later. When the water was cold, and the LED was off, I nudged the temperature setting dial on aquastat, and it immediately turned on.

    I suspected the aquastat (as did Bradford White) so I replaced it. Since there was no thermal compound in the well, I suspected very bad thermal transfer between the water in the tank and the bulb of the aquastat. Since I put a new aquastat in and put in thermal compound, I'm stymied. Hard to believe I have 2 bad aquastats.

    The possibility of packing styrofoam inside the tank sounds like it could cause this.

    Tomorrow, I'm going to repeat my test with a voltmeter on the aquastat terminals to see if it is really not closing when the water gets cold.

    Thanks again for the help.

    ~~Andy
  • hot_rod
    hot_rod Member Posts: 22,268
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    What boiler do you have? Many of the new boilers allow you to run the indirect from the boiler control, with a sensor in the tank.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HVACNUT
    HVACNUT Member Posts: 5,865
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    What model aquastat?

    It's very odd that it will have both a major delay and a major override. Could both aquastat wires be cut and intermittently short and open to each other? Stranger things have happened. 

  • PC7060
    PC7060 Member Posts: 1,174
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    154F at the (sink) tap is very high and is dangerous for young children. Are you referring to the drain on the tank? 
  • Derheatmeister
    Derheatmeister Member Posts: 1,550
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    Boiler,piping and control strategy could be a large piece of this Puzzle.
    Could you post some Pictures of your mechanical Room ?
  • yellowdog
    yellowdog Member Posts: 157
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    whats the possibility of the well for the aquastat being scaled up and delaying the water temperature from transferring thru the well?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    The other question is is this a new install? Or is this been installed a while and just started acting up? Did it ever work right?
  • mattmia2
    mattmia2 Member Posts: 9,753
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    You might also call Bradford White and ask them what a defective dip tube would do

    I think the dip tube is broken so the cold water is going directly from inlet to outlet while the tank stays hot. When the outlet gets cold, measure the temp at the well and the coil connections and the drain. I bet the tank is still full of hot water.

  • andycoop
    andycoop Member Posts: 7
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    I ran a few more tests today.

    I opened the loop by disconnecting the aquastat from the rest of the heating system. I connected the wires that were going to the aquastat and the system turned on immediately. The Taco relay showed the water heater was calling for heat, and the circulator pump was energized, and the boiler turned on. That tells me there is no delay in that part of the system and it is working properly.

    I then connected an ohmmeter to the aquastat terminals, which showed open since the water was hot. I measured the water at the tap and it was 145 degrees. I ran the water at the tap until the hot water was used up and the temperature came down to 100 degrees. I drained off a gallon of water from the bottom of the tank and it was 102 degrees.

    This leads me to believe that the dip tube is ok. What do you think?

    I then waited 90 minutes and the aquastat was still open. I drained off some more water until the temperature was down to 70 degrees, and it was still open. 15 minutes later, the aquastat closed.

    Sure looks like there is very poor thermal conductivity between the water in the tank and the aquastat, but how? And how would I find out what it is and fix it?

    I'll respond to some of the previous questions:

    >>"It's very odd that it will have both a major delay and a major override."
    What do you mean by a major override?

    >>154F at the (sink) tap is very high and is dangerous for young children. Are you referring to the drain on the tank?
    I measured it at the tap. I agree, and my next call is to Bradford White, as this is a dangerous problem. Luckily, there are no young children around, but we still have to be careful.

    >>whats the possibility of the well for the aquastat being scaled up and delaying the water temperature from transferring thru the well?
    That is what I think is happening, but what would cause this, and how would I fix it?

    >>The other question is is this a new install? Or is this been installed a while and just started acting up? Did it ever work right?
    No, this was installed in 2016. I don't believe it ever worked correctly, but since it kinda worked, I never noticed it. There were a few clues. I ran out of hot water once or twice, and noticed that even though we were out of hot water, it wasn't calling for heating the water.
    Also, since Covid I started working from home and my office was directly over the boiler. I noticed in the summer, when the boiler is only used for hot water, that it turned on hours after we took our morning showers.

    Since there is a delay on both ends of the temperature scale (turning off and turning on) the temperature swing is very large. Also, since it heats up quicker than it cools down (when not actually using the hot water), that delay tends to skew the temperature range to the hot side. That's why it looked like it was working.

    Once again, thanks to all for your expertise.

    ~~Andy
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
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    Either you have a well adaptor that is not transferring the water temperature from the water in the tank to the perfectly good aquastat, OR you have a defective aquastat.

    Can you describe the well adaptor (that's where the auqastat sensor is measuring the water temperature?)
    How far inside the tank does the well adaptor reach? Is it located on its own tapping? Is it located on a Tee fitting where something else is connected? Is it welded into the tank? Is it removable? Is it possible to post a photo from you smart phone? If this is not possible, can you at least give us the model number of the DHW indirect tank, The part number of the Aquastat, and the model number of the heating boiler.

    I'm thinking that there is something not right about what you have, but it is difficult to diagnose from the words you have offered so far?

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    Larry WeingartenMikeAmann
  • mattmia2
    mattmia2 Member Posts: 9,753
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    I just don't see how something would keep the well hot for hours without it being surrounded by hot water. I would try to take the temp of the tank in the middle somewhere like maybe near the upper coil connection.

    I wonder of the zone valve isn't sealing and hot water is flowing through the coil and keeping the aquastate hot somehow.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
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    I looked over your original post and found that you did offer the model number of the water heater. Can you verify that the aquastat is located in the factory recommended location? (Red Arrow)

    In order to determine what is causing the temperature in the tank and the sensing bulb to be so far off, can you remove the well adaptor and inspect it? You will need to drain the water from the tank to do this.
    This illustrates what I woild look for once you remove the Well Adaptor from the tank.
    The aquastat that Bradford White furnishes with that tank has a fixed differential of 10°. So when the water temperature in the tank reaches the set point (say 120°) the heating coil in the tank should stop getting hot boiler water circulation. The circulator pump should stop. When the water temperature at the aquastat location drops and reaches 110° the pump should start pumping hot boiler water into the boiler water heating coil in the water heater.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    Larry WeingartenMikeAmann
  • andycoop
    andycoop Member Posts: 7
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    The water heater is a SW280L by Bradford White
    The aquastat is a Honeywell L4006A. The original one was a Honeywell brand, the replacement is a Resideo, same model number. They both exhibited the same symptoms, and it is possible that I got 2 bad ones. I did test the original one in a pot of water, and it worked fine. The switch opened and closed at the correct temperatures and there was no lag.
    The boiler is a Crown CXE-6, although I see no problems with that.
    When I installed the aquastat, I stuck in a 6 inch screwdriver, and didn't hit the end, so it is longer than that.
    I don't know how the well is attached. I'll add a picture, but it really doesn't show much.

    ~~Andy
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
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    The Well Adaptor is this part here. You remove it by turning it counter clockwise. MUST HAVE NO WATER IN THE TANK.

    After inspection of the exterior of the well, look inside the hole to see if there are any unusual things inside the tank that might block the heat from reaching the well adapter

    I also see an adjustment for the Aquastat Differential. This white dial here. You may want to set this at the lowest number for now.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    MikeAmann
  • andycoop
    andycoop Member Posts: 7
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    The differential dial is set to minimum, and it was for both aquastats.

    I don't feel comfortable removing the well adaptor myself. I think I'll leave that for the professionals. Since this is under warranty, would you suggest calling Bradford White first, or should I just let my plumber do it?

    Thanks.

    ~~Andy
  • mattmia2
    mattmia2 Member Posts: 9,753
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    I'd measure the tank with a thermometer in a few places first. I can't see how the well is staying 40 degrees above room temp unless it is immersed in water around that temp.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
    edited December 2022
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    Under Warranty!!! Definitely have the installing plumber figure this out. You have water that is TOO HOT at times and you have no hot water other times. This is definitely an issue for the Installing plumber to solve.

    You just need to keep calling with a "No Hot Water" call and/or a "Water Too Hot" call as it occurs each time.

    The plumber will get tired of your calls soon and solve the problem.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    Larry Weingarten
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,338
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    Hi, I'll add this tidbit. Feel with fingertip the part of the brass well that you can see. Do this at different times to see if it conforms to what the aqua-stat is telling you. Brass is conductive enough so that if it's only warm to the touch when you have 150F water in the tank, that's a good clue that something is preventing heat from getting through. If this is a glass-lined tank, the anode may have precipitated a coating of calcium around the well. Shouldn't happen as there should be a plastic liner, but those can fail.

    Yours, Larry
    Alan (California Radiant) Forbes
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    @andycoop

    Check to make sure the aqustat bulb is pushed all the way in until it bottoms out in the aqustat well. If it's pulled back a little it could be part of your issue
    MikeAmannkcopp
  • hot_rod
    hot_rod Member Posts: 22,268
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    Pull the aquastat out of the well, use a hair dryer, hot, then cold air settings, and see if it responds

    Occasionally wells scale with lime, usually delaying the temperature response, but not stopping it
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    The drawing @EdTheHeaterMan posted of the indirect shows the tank tapping to be 3/4" NPT so that well can be taken out and checked and the dip tube could be viewed
  • tim smith
    tim smith Member Posts: 2,765
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    When you drained water off bottom and read 102 but aqua stat not closed. What was aqua stat set for?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
    edited December 2022
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    I still believe this is the installing plumber's problem. @Larry Weingarten @tim smith @EBEBRATT-Ed and @hot_rod, You can suggest all the testing and diagnosing you want, but the installing plumber still is the one who has to make it right. The squeaky wheel gets the grease. A phone call to the plumber every time the water is too hot, or is too cold, is appropriate, until it is fixed. That may be 2 or 3 calls a day. Just keep the plumber updated with each condition in real time.

    You will either get him to fix it, or piss him off so much that he will stop answering your calls... If that happens, then the manufacturer gets the calls. If they don't help then the lawyer gets the call. I'm retired and have all the time in the world to sit on hold... I realize you probably don't. Perhaps you have a parent or uncle that is in my situation. Ask them for help staying on hold while they complete their retirement hobbies.

    As a side note to this, My son had an issue with Comcast/Xfinity who swapped out his plan to save him 15% because of a sales initiative. His bill ended up going from $299.01 a month to $324.00 per month as a result of removing and replacing different services ...long story... but the bottom line is: I bugged Comcast/Xfinity for 3 days (not in a row) and his final package with all the services he had before the internet failure that started this mess, happened the beginning of December, is now only $273.00/month. I had the time to wait for the answer on the phone. I got each persons name and employee number, as they made their notes in the system. As the next person started to fix the problem, I referenced the date and the Comcast employee to the CSR I am speaking to, so they can see what the concern was. That saves time when you have accurate records.

    This sounds like you need to be the squeaky wheel.

    Just an old man's thoughts on the subject.

    Mr. Ed

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    Alan (California Radiant) ForbesMikeAmann
  • hot_rod
    hot_rod Member Posts: 22,268
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    No harm in checking a few simple things that Andycoop might be able to deal with on his own, since the repair guy doesn’t seem willing or able to address the problem
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • andycoop
    andycoop Member Posts: 7
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    >>When you drained water off bottom and read 102 but aqua stat not closed. What was aqua stat set for?

    115 degrees. It was also set to 115 when I read 145 at the tap! Hence the problem exists at both ends of the temperature range.

    Ed: The installing plumber is long gone. I have a competent one that has been working on this. I chased this with the manufacturer first since it is under warranty, and it looked like a manufacturing issue. They already admitted that the well should have had thermal grease in there, and it clearly did not. I'm going to raise the safety issue Tuesday, and see if it gets their attention. They've been responsive so far, they just haven't found or fixed the problem.

    I don't mind checking the electrical stuff (I'm an EE), but stay away from plumbing stuff that I might not have the parts to fix.

    Thanks to all.

    ~~Andy

    EdTheHeaterMan
  • mattmia2
    mattmia2 Member Posts: 9,753
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    Was the 154 immediately after the aquastat ended the call? If the zone valve isn't closing and it is heating with the heating zones too that could explain your temp swings.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
    edited December 2022
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    @HVACNUT that is a good call. WOW :o You have a good eye to find that detail.
    @andycoop Look at this illustration closely.According the the picture you posted and what HVACNUT enlarged, your sensor bulb is not inserted far enough. The tailpiece of the capillary tube is located where I have placed the Blue Arrow. If you can get the sensing bulb pushed in farther, then the sensor will be more responsive. See the location of the capillary tailpiece with the RED arrow.

    This is done by removing the L4006 aquastat from the well adaptor, making the capillary tube as strait as possible. inserting the bulb in at least 3" deeper that you have it now. Use a thin flat head screw driver to carefully push the sensor bulb past the Honeywell 107408 compound. If you put too much 107408 compound in there, It may be difficult to use just the capillary tube now. After you are sure that the sensing bulb is all the way in, then you will get a better temperature response from the control.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    MikeAmann
  • hot_rod
    hot_rod Member Posts: 22,268
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    Make sure the small copper tube is not kinked or broken. It is a fluid filled tube, not a copper wire.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterManmattmia2
  • tim smith
    tim smith Member Posts: 2,765
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    I agree with hvacnut I dont think the bulb is pushed all the way in. I would like to see how much capillary is still in the control. It may be there is dried out conductive compound in the well. Seen that many times. Sometimes have to ream out with stainless tube brush.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    I posted about making sure the bulb was inserted 12 posts back.

    This is a common problem and helps more that the heat transfer paste.

    Many time the capillary is coiled up and will not bottom out especially in an extended well.

    People inset it and it doesn't bottom out.

    You have to uncoil the capillary first then make sure it bottoms out
    MikeAmann
  • mattmia2
    mattmia2 Member Posts: 9,753
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    A drill bit turned by hand would work to ream out the hardened compound
  • HVACNUT
    HVACNUT Member Posts: 5,865
    edited January 2023
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    @HVACNUT that is a good call. WOW :o You have a good eye to find that detail. 
    Thanks Ed! Mommy drowned the dumb ones.

    As I was writing about the well, and whether it could be a sensor well, I scrolled back up to see if it looked different than a standard well. And there it was.

    I'm reading a book and there was a good quote. "When you hear hoof beats, you think Horse. Sometimes you have to think Zebra."
  • psb75
    psb75 Member Posts: 845
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    I'm going to second that to @HVACNUT--Good eye! Occam's Razor once again cuts to the "quick"...and EASY!
    "Where" indeed is the larger portion of the capillary tube? Is it coiled (crammed)in the upper portion of the aquastat box and perhaps kinked?
    MikeAmann