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Too damn hot water? WM ultra 155 series 2 boiler with w/ gold plus 60, series 3 indirect fired wate

Trouble here relates to an earlier posting (to which I added this info.: https://forum.heatinghelp.com/discussion/comment/1687064#Comment_1687064

Apologies for any repetition.

Washing the dishes one day the hot water was too damn hot! Measured the temp @150 +/-. This was new.

Tried to adjust the temp by turning down the dial on the tank top with no result. Tried raising the thermostat/aquastat (thermistor?) in the drywell tube(?) with no material change. Went to the manual and found the documentation a little cryptic for my (inexperienced) eyes I did check continuity of the therrmistor which checks. Elsewhere here I tried to find enlightenment but got stumped about testing the aquastat more completely.

I further turned down the dial and raised the aquastat with no material improvement.

Two days ago the boiler shut down due to error 37- Return water temperature sensor open circuit. Needed manual rest which I did and now works with the same results.

The replacement part 635-600-063 (from Manuel) includes the dip tube and cost in excess of $380. Elsewhere I found 633-900-130 Residential Thermostat Kit for Weil Mclain indirect heaters for $135 ,no dip tube, which sounds like a bargain.

Any words of caution?

TIA Stephen


  • stephen11962
    stephen11962 Member Posts: 40
    Should have added:
    WM ultra 155 series 2 boiler with w/ gold plus 60, series 3 indirect fired water heater
  • rick in Alaska
    rick in Alaska Member Posts: 1,457
    edited June 2022
    Is there a mixing valve on it? And if there is, how is it piped? If the mixing valve is above the tank, they have a tendency to cause the water to be really hot ( the tank temperature) until it cools back down. There is a possibility you have a bad mixing valve, but my experience is that you have a bad thermostat in the tank.
    Pictures of the install would help.
    Just noticed the link with your pictures. Unless the piping from the boiler is somehow pushing in to the tank on a heat cycle, replace the thermostat. Pictures of the boiler piping to the tank would help.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    edited June 2022
    As I recall, The Plus 30, thru the Plus 80 indirect water tanks were notorious for having a leak at the thermostat well. The plastic around that well formed a sort of tub that the actual thermostat control would sit in. When the leak filled the tub, the control contacts were under water. Eventually they would rust or corrode together causing the water heater to call for hot water indefinitely. This would cause two problems.
    A. Excessively hot water because the boiler never stopped heating the DHW tank. AND...
    B. The call for hot water priority would cause the space heating circulator to stay off until the hot water demand was satisfied. Therefore you would experience no heat also.

    As far as the 155 boiler was concerned, there was no reason for an error code because that part of the system was working as it should. The occasional error for a return water over temperature might happen but it also may not. And the trouble shooting will not refer you to the DHW temperature control.

    First, disconnect the wires to the thermostat.
    Next, take the thermostat off the top of the tank.
    If the thermostat is water damaged then
    Third, replace the dip-tube and thermostat (or replace the complete tank with a Buderus or Crown) or any other brand where the thermostat is mounted on the side of the tank.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • kcopp
    kcopp Member Posts: 4,397
    that aquastat was different than most. I have had issues over time w/ them failing (not a leak) but having issues w/ not being accurate... and yes overheating.
    rick in Alaska
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    There was one thing that i liked about that thermostat. No numbers! There was a blue section the gradually changed colors to a red section. You would point it to a space in the middle and see what the water temperature was in an hour or so. If the water was too hot you turned the dial a little to the blue. If it was too cold you turn the dial a little to the red.

    Numbers on a dial are meaningless but can be a cause for so many nuisance service calls.

    So my question is: Does the thermostat shut off the DHW circulator off when you turn it down to a lower temperature? If it does then lower the dial to a comfortable "ACTUAL" water temperature, and pay no attention to the numbers on the dial (if any).

    If the thermostat can not turn off the DHW pump by lowering the dial, then replace the thermostat.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • stephen11962
    stephen11962 Member Posts: 40
    I like what you said.

    The themistor/resistor is not open, shows a resistance. The DHW circulator turns off, albeit at a very high temp. The dial goes from LOW to HOT. The dial was set to 4th(?) division on the low end of scale.

    I have set the dial just now to the letter L of the word LOW on the lowest setting. I will check out the temp later today and report back.

    If this does lower the temp to acceptable range I still wonder if thermostat is reliable. The problem is new after 13 years! Any thoughts?

    Thanks much, maybe the beginning of the end.
  • pecmsg
    pecmsg Member Posts: 4,704
    ASHRAE recommends water heaters maintain 140*f minimum to control Legionaries disease. 
    Then a mixing valve is installed to lower the point of use to less then 120*f
  • mattmia2
    mattmia2 Member Posts: 9,475
    How is the boiler controlled, is it cold start or warm start?

    How is the zone for the DHW controlled, is it zoned with a zone valve or is it zoned with a circulator?

    Did you use a meter to determine if the aquastat in the indirect is calling for heat with it turned down? Either measure the voltage across it, it should be around 24vac when it is open and nearly 0 when it is closed and calling for heat, can also disconnect the control wiring and measure it with an ohmmeter.(assuming it is an aquastat, if it is a themristor then you will have to give us more information about what it connects to)
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    edited June 2022
    I like what you said. 

    Well that makes at least one, thank you Stephen!

    It could be the beginning of the end of that particular thermostat. 

    Or is it possible that someone inadvertently increased the temperature? Depending on the location of the dial, a repair man running a cable wire for that 82 inch flatscreen may have bumped it. Or perhaps a refrigeration tech who was servicing the cold room for your $50,000 wine collection.

    Either way, you will know by tomorrow if the adjustment solved your problem. When your wife screams from the shower because the water is too cold, you will know that you need to turn the dial a little warmer! 
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • stephen11962
    stephen11962 Member Posts: 40
    Latest info:

    The aquastat does work, it will lower and raise temp of DHW just not how in previous 13 years; at first div on dial water was 122*, at lowest possible setting 115*. I am trying by steps to find the "ideal" temp.

    But with the latest experience I worry about the longevity of the aquastat into the future. I am thinking of getting a new aquastat never mind the expense.

    I do live in a neighborhood where $50,000 wine collections are even popular, but not chez nous. And no repairmen have been in the house just before the onset of the problem.

    Cold/Hot start boiler control: This is a new subject for me. The boiler is a high efficiency modulating boiler that is almost always "warm" since it supplies heat for DHW. Not sure if that is an answer.

    I hope this is the last of this subject. I would like to thank the helpful responses from everyone. It is a confirmation of the generosity of strangers!

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    You have a good idea in getting a replacement DHW temperature control. Just having it there, in the event that the existing one is failing as a result of a slow acting defect with the calibration of that part. The other possibility is the that elusive gremlin that goes around the house hiding your keys or loosing the remote control. I call that gremlin in my home "The Grandson". ...But, I wouldn't get rid of him for all the gold in the world.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • mattmia2
    mattmia2 Member Posts: 9,475
    What series/model boiler is it? warm/cold start just applies to cast iron boilers.

    Are any other zones heating when this happens or is all the domestic heat off for the summer?

    I was thinking it was still heating after the call from the aquastat on the tank ended but the boiler would still have to be hot for that to happens. If the controls run a significant post purge of the dhw circulator after the call ends that can cause significant overshoot depending on the mass of the boiler and the setpoint of the boiler for the dhw call.