Melted Top T-stat

The Tank Melted Top T-stat

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  • #20238
    seattlesteph
    Participant

    Bradford & White Model M250S6DS2 Electric 40 gal tank installed December 2004.
    Suddenly water at tap was 170 F. I knew that I had issues, so watched carefully. It did not get any hotter. Two weeks later: no hot water.

    Tested everything with multimeter: everything ok except the top T-stat. Replaced top T-stat with identical model. Everything tested good. And good hot water supply.
    A few weeks later I ran two consecutive large loads of wash on HOT. I live alone, generally wash clothes in cold, and use very little hot water, so this was an unusual load – perhaps the first such since the tank was installed.

    I don’t recall if it went through the too-hot stage again, but a couple days later there was no hot water.
    Breaker was ok, so I pressed “Reset” on the top T-stat, which clicked.
    A couple hours later, I smelled classic “hot wires/ melting plastic” stench, traced it to the WH, so threw the circuit breaker.
    The center of the t-stat had melted, all around the temperature adjustment knob, which had fallen off.
    Assumed that maybe I had not cinched the screws down tight enough, so expected tarnished wires from a short. But the wires were all bright and shiny. The tarnished screws on the T-stat were the one adjacent to the adjustment knob and the one just above it, neither of which has a wire, and the one above it – but its wire was shiny.

    Replaced top T-stat again, being careful to double check the wiring diagram and to cinch down the screws.
    Ran the washer with 2 consecutive large hot loads, to see if I could trigger the failure again. But it seemed to be ok. Good hot water supply again.

    Took the melted T-stat around to the electrical/plumbing folks in the area, to see if anybody had any ideas about what might be going on. The store I had bought them from offered to replace it as defective. But I had already bought and installed the new one.

    A few days ago I drew about 10 gallons from the hot tap.
    The next day the water temp at the tap went up again, and then the temp at the tap started dropping – luke warm now.
    I have just retested everything: elements are good, both T-stats test good.

    But I am reluctant to push the reset again without testing or checking SOMETHING else that I had not checked the first time.

    Who’s got a good idea for me? Any idea?

    #20239
    Larry Weingarten
    Participant

    Hello:If there is ANY moisture around the thermostat, it will corrode the contact points in the switch. This leads to arcing and/or the points welding together. I suspect this is what you found… basically the switch burned up.

    So, do you see any moisture? It could be something leaking under the jacket or water dripping down from above.

    Yours, Larry

    #20240
    seattlesteph
    Participant

    Thanks, Larry. Good thought. The tank is in my bedroom clothes closet – very dry environment. Dry tank insulation. I just ran my finger across the tank, underneath the insulation, all around the t-stat: no moisture at all. – Steph

    #20241
    Larry Weingarten
    Participant

    OK: Next is to make sure the wiring is done right, by finding a wiring diagram: http://www.bradfordwhite.com/sites/default/files/product_literature/238-47104-00A.pdf and tracing lines down. It shouldn’t have changed, but best not to assume anything. Then, is there any evidence of voltage spikes? Flickering or overly bright lights? Next, is the upper element the same size as the name plate says? If it’s bigger, it could be adding load the switch wasn’t designed for. A band-aid fix could be to install a smaller element, but I’d rather know just why the thermostat is failing.

    Yours, Larry

    #20242
    seattlesteph
    Participant

    Hi, again. I kept a diagram as I removed the first one. It matches exactly the diagram inside the panel. It is two-element, non-simultaneous. For this exercise, I just went in and physically touched each wire as I counted it off on the diagram. It is ok.

    Voltage spikes? Weeeehl, we’ve had some storms. One included lots of lightening bolts in the area – very rare for here. Don’t have a clue as to the chronology. But there had been none before the first T-stat failure, And there was non prior to the most recent “failure.”

    The label on the tank says that each element is 4500, with a total of 4500. I do not see any indication of size on the element itself. How might I check that?

    I am intrigued by the preliminary excessive heat for a period of days prior to the first failure: I have had tenants tell me that that had happened to them: a period of time with too-hot water, followed by no hot water. I have always just replaced their tanks. It must be a common scenario, eh?

    I see in the manual that you sent me – thank you! – the mention again that “It is important that the entire back surface of the thermostat is in full contact or flush with the tank. Improperly mounted thermostat will lead to improper heater operation.” Mine is not flush: it tips out very slightly towards the top. It may have been flush prior to the first failure – I did not check. Could that create the issue I have?
    Thanks for all your time, Larry!

    #20243
    Larry Weingarten
    Participant

    Hello: When elements are behaving, they have the voltage and wattage printed on the side of the dark plastic “cap” that lives under the two wiring screws. There should be something like 208 volts – 3800 watts on one side and 240 volts – 4500 watts on the other.

    Overheating can be caused by the element failing with a leak to ground, but I’ve never seen that affect the thermostat/s. If the upper thermostat were not in contact with the tank, it would remove thermostatic control AND the high limit! That’s called a bomb 😯 It wouldn’t damage the thermostat until it all went kablooie. Fortunately, yours didn’t do that. Yours pretty clearly had an electrical malfunction.

    There should be a piece of fiberglass insulation over the thermostat and under the cover plate. This keeps the thermostat at basically the same temperature as the tank. That insulation often goes missing, but I’m running low on ideas about why you’ve had two thermostat failures. They seldom fail. I suppose if they had been stored in a damp place and had internal corrosion when you got them…. but that’s a stretch. I gotta ask: There isn’t anything else on the water heater circuit is there?

    Anyway, should your new thermostat fail, I’d look for a replacement from a different source, located somewhere in a dry desert. 😉

    Yours, Larry

    ps. Please do keep us informed. It’s a puzzle.

    #20245
    seattlesteph
    Participant

    Thanks for your interest, Larry.

    OK. I expect to be in the house the rest of day. Just threw the breaker, clicked the ECO, and the heater started up.

    Set at 120, about how long do you think it might take for the upper t-stat to be satisfied?

    How can I tell if T2 opens and T4 closes? How can I tell if the lower element activates?

    If T2 opens, and T4 does not close, the lower element will not activate, and I will just have a limited amount of hot water, right?

    If T2 fails to open, the upper element will just keep heating until all the water in the tank is hot, and…..?

    #20246
    Larry Weingarten
    Participant

    Hello: You can use a meter to see where the power is, or just turn the upper element up or down and listen for it switching power to the lower thermostat or upper element. If the lower element is working, you’ll feel the tank is warm lower down. You can confirm these things with your meter. Just avoid those live wires! 😯

    Yours, Larry

    #20248
    seattlesteph
    Participant

    But how can I tell the first time?

    If I turn it up, the upper will just keep working. If I turn it down, the upper will just stop working. Or what am I missing?

    It has been two hours, and the tap temp is at 115. The t-stat is set at 120 plus a smidge – it used to get me 125.

    At what temp do you think it should “be satisfied,” close T2, and open T4 to switch to the lower?

    #20249
    Larry Weingarten
    Participant

    Hi: If the top of the tank is say at 110 and you turn it down below 110, it will throw power to the lower thermostat. As it’s at 115 now, you should be able to turn it down and hear the click that lets you know power has been switched to the lower thermostat. From there, turn the lower to 120 or wherever you wish to heat the entire tank.

    I am a bit confused though. The upper should never need to heat for two hours. There isn’t that much water. Makes me think there is an upper element problem. Have you tested it for leaks to ground?

    Yours, Larry

    #20250
    seattlesteph
    Participant

    OK. It has been four hours.

    Temp at tap is on target at 125.

    When I turn it up to 140, there is a loud pop and additional hissing – I guess that is the lower kicking in, eh?

    No hot wire/melting plastic stench. This is very good news. Maybe the melted t-stat was just due to a power surge during that storm? I had turned off all electronics when it started.

    I am concerned about your observation. I’ll go follow your instructions, and will report back – probably tomorrow.

    Many thanks for the hand-holding, Larry.

    #20252
    Larry Weingarten
    Participant

    Hello: Something is still wrong. There should be no loud pop, just a click and the hissing should only be something that can happen after an element is heating… starting up gradually. It could be hissing or singing or just quiet. It should not be the sort of hissing that happens when arcing is happening at burning contact points. 😕 You’ve got an interesting heater!

    Yours, Larry

    #20253
    seattlesteph
    Participant

    Good morning. So, I threw the breakers off, set the m-meter at 1k, and placed one probe on screw and one probe on the inside-most layer of metal I could reach – assume that is the actual tank. No movement at either screw of either element. (Yes, meter zeroes out, and I had the covers off the probes!) Also tried grounding to each of the three copper pipes: Nothing.

    I’ll agree that what I called a loud pop is actually a click that I had not been expecting right next to my head. The hissing starts a few seconds after it clicks when I turn the t-stat back down – it is coming from the upper portion of the tank.

    But, if we attribute the melted t-stat to a power surge, your decription of the symptoms of a grounded element sound right on: “water getting exteremely hot and reset button popping out.”

    Could the grounding be intermittant? Or at an early stage of development that does not register yet?

    In the first event the tap temp went to 170 and stayed steady for several days. In the second incident, I did not check the tap temp – it was just hotter than usual. In the most recent event, it did not get all that hot and was extra-warm for only a couple of days before the reset button popped. Could it be progressing?

    #20256
    Larry Weingarten
    Participant

    Hello: More than one thing may be wrong at once. It sounds as though the upper element is behaving. Now, I’d look at the lower thermostat and check the lower element as well. One of them might not be working correctly. They could cause some of the symptoms. 😛

    Yours, Larry

    #20261
    seattlesteph
    Participant

    OK. I’ve run back through all the electrical tests – all ok.

    So I am running a couple of empty washer loads on hot, to see if I can trigger the reset button. I’ve also set both t-stats higher than usual – about halfway between the lowest and the highest settings.

    One thing I noticed is that when I turn the lower t-stat adjustment dial back and forth, the click is very faint compared with the upper one – is that typical?

    If the lower t-stat were not working, it would just allow the lower element to keep heating, right? Or?

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