Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Superstor 40 Gal. Tank control issue

It is not uncommon for the aquastat to be defective. I have had to replace brand new ones that were bad. Johnson Controls has a cool digital one that cost no more than a standard aquastat.

Dave Stroman, Denver

<A HREF="">To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"</A>


  • Jake_5
    Jake_5 Member Posts: 1


    I have a 40 Gallon Superstor Stainless Steel Tank and the
    temperature is set on 120 degrees. The boiler
    is constantly going on and off. Its summer so I have the
    heat off, so I'm wondering why the boiler's always
    going on. I emailed the company and they said it was a 'control issue' not a tank issue.
    Even if we just take one 5 minute shower it still goes on.
    Shouldn't the tank store more hot water than that?

    Thanks for the help
  • carol_3
    carol_3 Member Posts: 397

    My guess is that what you're seeing is a result of the normal "differential" in your water heater temp control. In order not to have the unit go on and off a lot, in a water heater there's usually 15-20 degrees difference between the hottest the water gets heated to, and the lowest temp the water can drop to before the burner comes on. So let's say (I'm just picking numbers here) your water heater's range is a low of 120 degrees and a high of 140. So it's summer and the temperature quite slowly drifts from the 140 the last time the burner came on (maybe hours ago) down toward 120. Let's say the temp is 122 when you start your shower. When you start the shower that water is replaced with cold water, which brings the tank temp down below 120. The burner comes on and takes the temp up to 140 (again I'm just picking numbers out of the air). If there's no other draw of hot water, the burner may not come on again for hours. If there are lots of showers, and other appliances, it may come on sooner.
  • Brad White
    Brad White Member Posts: 2,393
    It also may be

    a function of the water volume in your system (coupled with differential issues as Carol described).

    Is the system close-coupled with relatively low water volume?

    Say the total water volume of the Super-Stor coil, piping to the boiler and the boiler itself is maybe 5 gallons (that is the equivalent of less than 120 feet of one-inch copper pipe mind you). Made up but an order of magnitude. You can see how easy it is to have that, even with a lot of piping-equivalence.

    Say also that you have a 120 MBH output boiler while we are at this. (Curious- mod-con or cast iron? High or low volume?)

    If your circulator feeding the Super-Stor is maybe 10 GPM or near what HTP recommends, your total through-put of water, the total circuit volume, will be about 30 seconds.

    You may start feeding the heater on a cold start at near room temperature, taking the full boiler output.

    But once the boiler is up near it's operating high limit, say 180 degrees, that 10 GPM which at first was delivering the full boiler output at say a 24 degree drop narrows to maybe a 5 degree drop. In at 180, out at 175 and your boiler hits the high limit very quickly at full input.

    Check your flow rates, boiler settings and tank settings, see if you cannot get more run-time and less cycling. You may have to reduce your flow rate on your boiler-side circulator too, in order to raise that delta-T. A lot of variables, I know, but a good place to start.

    Worst case is, you may need to add a buffer tank.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • hr
    hr Member Posts: 6,106
    Or the aquastat differential

    is real tight. I've seen some as low a 5 degrees between on and off.

    hot rod

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    New addition ?

    Whats the operating control on the boiler itself? Did you have a tankless coil before and the plumber installed this tank and removed the coil? The question is, did he change the operating (aquastat) control.

    Tell us the control number on the boiler and we'll be able to help you better.
  • Paul Rohrs_4
    Paul Rohrs_4 Member Posts: 466

    more information, my guess is that the Grey "TT" wires are tied together and it is running up to temp, shutting off, and starting up on it's differential. (Again, this is assuming you have an HTP boiler tied to your HTP indirect)

    No Vision 1 package? There is a "Guy" around here who does the same thing that we are constantly correcting.

    Even though there is no space-heating call, the jumpered TT presents a constant call for heat even if the DHW is not calling. Is this a high-temp system?


  • tim smith
    tim smith Member Posts: 2,421
    Cycling on and off

    It also is very likely you have a recirc pump on your hot water pipe system. This circulates water around the house to fixtures so hot water is ever present. In turn, this ejects heat off all that piping and cools down the tank and causes it to come on. Just a thought, Tim. PS, you could put a timer on recirculation pump so it is on only during main useage times. Good luck
  • Weezbo
    Weezbo Member Posts: 6,232
    it may be....

    that there is no dedicated pump in the tank supply side from the boiler and it is controlled by a zone valve, the zone valve might be defective causing that problem.

    another possibility is that there is on demand hot water recirc system that is coupled with the system that is left to run unregulated,...too great of a temp diff from potable supply water and the tank temp, anti scald valve in the mix,...there might be an additional control on the boiler that in conjunction with any one of the above might cause the boiler to fire depending upon the piping arrangement and the control.
  • Ted_9
    Ted_9 Member Posts: 1,718

    Was the water heater working fine and did it suddenly call erratically? If so what has changed? Has a technician looked at it yet?
  • rob brown
    rob brown Member Posts: 69
    i agree

    with tim.if you have a recirc system, your tank temp drops pretty quickly. if the hot water pipes are not insulated(recirc too),then you get the pleasure of paying to air condition all those excess & expensive btu's back out of your house. timers help but i like the motion sensor to activate pump the best. very slick. if there is no recirc, i would check for heat migration out of tank after long period of non-use. if the hot feed pipe is hot 3' away from tank, you might want to find out why. rob
This discussion has been closed.