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

Hot water runs out after indirect empties

Very frustrating. I have a gas burner that always stays at 170° and a superstore indirect 45 gallon storage tank. The 1 inch pipes going to the indirect are always very hot. The output to domestic the three-quarter inch pipe is very hot for about 15 minutes I’m guessing due to the fact that the indirect hot water is used up. So for whatever reason the gas burner is not refilling the indirect with new hot water to continue. I spoke with the manufacturer at HTP and they said scale is the issue. We do not have hard water here at all and I believe that is not the issue. The indirect is about five years old the gas burner is about 10 years old. Thank you if anyone has a suggestion so my wife stops yelling at me I would really appreciate it. 
«13

Comments

  • JUGHNE
    JUGHNE Member Posts: 9,756
    How many pumps are on your system?
    One or more for heating the house and another for heating the indirect?
    Is the pump for the indirect running?

    Can you post pictures showing boiler and tank, back up to show piping and pumps.
    kcoppcoby
  • JUGHNE
    JUGHNE Member Posts: 9,756
    edited February 2021
    My best guess is that the pump is not running as it should.
    The pipes are hot from the boiler and the little DHW produced is from gravity flow between boiler and tank.

    The boiler is high firing to produce DHW but failed to turn on the pump.....maybe.
    STEVEusaPA
  • HomerJSmith
    HomerJSmith Member Posts: 1,562
    edited February 2021
    What manufacturer of boiler? Is this a new problem? I the indirect communication with the boiler with a sensor or mechanical aquastat? Does the tank have a tempering valve on the hot water output? A pic of the boiler and indirect hookup would be most helpful.

    I have a 45 gal HTP and I never run out of hot water.
  • mattmia2
    mattmia2 Member Posts: 5,510
    Is the water coming out of the indirect not hot or simply not as hot? In addition to what type of boiler is this, what size is it, BTU/hr input and output?
  • Denniss516
    Denniss516 Member Posts: 35

  • Denniss516
    Denniss516 Member Posts: 35
    I have three circulator pumps one for the indirect and the two others are for two zone heating. The 1 inch pipes I believe you’re always hot keep in mind I have only been checking this while the hot water is running. My first guess is the aquastat it’s not working properly. It just seems that when the 45 gallon empties in the indirect for whatever reason is the boiler again stays 170° it doesn’t make sense to me that while the 45 gallon empties out the hot water is not replenishing in there. Last night my wife was in the shower I watched and felt all the pipes again and the burner never went on the 1 inch pipes were very hot the output again of the two domestic hot water got cool and the burner stayed at 170 never going on. Later on I tried the hot water again and it was fine. I’m guessing if the aquastat was bad why would it ever refill again in the indirect. This problem has been going on for a very long time and I have been overlooking it because I thought it was normal but after one of the people here in this thread said they never run out of hot water we do all the time as soon as the 45 gallons gets used. Again thank you very very much for your help
  • Denniss516
    Denniss516 Member Posts: 35
    I am assuming the circulator pump is good because when I feel both sides of it it is very hot and I also I’m pretty sure that I feel a hum on it when I touch it. The one zone of heat that we do not use for the basement it’s cold on both sides of the pipe which makes sense
  • JUGHNE
    JUGHNE Member Posts: 9,756
    Can you carefully (power off if you want) remove the cover of the aquastat grey box on the water tank and take a picture of the inside dial and the wire connections?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,188
    Those three circulating pumps are made by Grundfos. There may be a silver screw cap in the middle of the round side of the housing. that screw cap is there to check that the pump is actually spinning when power is applied to the pump. Those pumps sometimes get stuck and need a nudge. To do that you remove the screw cap, then take a pocket-size screwdriver (3/16" or smaller) and try to turn the inner impeller drive of the pump. Be careful of the small amount of water that may drip out of the opening when you remove the screw cap. It may be HOT.

    You will need to do this when the potable water in the tank is cooler. That is when the pump should be moving the boiler water in to heat the potable water. Once you complete checking the pump impeller drive to see if it is rotating, you can replace the screw cap. If the impeller drive was stuck and now is rotating, then you should have more hot water. If the impeller drive was not stuck then you have a different problem. Maybe air bound and only getting partial flow from boiler to tank, or the coil in the tank has a build-up on it as the factory suggested.


    Yours truly'
    Mr.Ed
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,188
    edited February 2021

    I am assuming the circulator pump is good because when I feel both sides of it it is very hot and I also I’m pretty sure that I feel a hum on it when I touch it. The one zone of heat that we do not use for the basement it’s cold on both sides of the pipe which makes sense

    That can be deceiving. There may be a gravity flow of the water from the boiler to the water tank. That gravity flow can account for some hot water but will not produce the rated capacity of the tank. Once the Potable water in the tank gets below the thermostat (aquastat) setpoint differential, the pump will produce as much as 8 or 9 gallons per minute (GPM) of flow from the boiler to the tank. Gravity will only move 1 or 2 GPM at most. making for a fraction of the water heater capacity to recover. Your hand is only a good thermometer for water temperature up to 120°F. Anything over that will be too hot to keep your hand on for any time without getting burns and blisters. So 130° at 2 GPM compared to 170°F at 8 GPM will make a big difference.

    Respectfully submitted,
    Mr.Ed

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,188
    edited February 2021
    Since this is an ongoing problem, you may want to check some other things.

    I have had an experience where the micro-bubble air-separator was clogged with mud all over the internal media screen. That would block flow for both heat and hot water zones but you may not realize it in the space heating mode if there is sufficient flow for that zone.

    I do not see any flow check valves on the system. They are necessary to prevent the reverse flow of the heated boiler water thru the zones that are off. Check to see if the circulator pumps have any indications that the check valves are internal check valves. There will be a designation on the nameplate of the pump. "IFC" is part of the model number of the circulator pump with Internal Flow Check valves. If a pump was supposed to have IFC and it failed or was never there, that may be your problem.

    I do not see an easy way to purge the DHW loop to remove air that can partially restrict flow. If the top horizontal pipe is only 1/4 full with 3/4 air in the pipe, that can also restrict flow.

    I have learned the hard way that you must provide adequate means of removing air when commissioning a new system. And sometimes we make mistakes. And sometimes we make mistakes that are left there as "good enough" because the consumer will never know the difference. I don't condone such practices, but I have come across jobs where others were left that way for one reason or another.

    Respectfully submitted,
    Mr.Ed
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • JUGHNE
    JUGHNE Member Posts: 9,756
    <b Last night my wife was in the shower I watched and felt......don't tell her that you told us that.....OK. ;)
    Now if it seemed time that the tank should get heat then the aquastat should have sent a call to the boiler and fired it up and turned on the pump to the tank.
    But you said with that condition of needing hot water the boiler did not fire, yes?
    So the signal from tank to boiler is not being complete.
    Show the grey box control I asked about.

  • Denniss516
    Denniss516 Member Posts: 35
    edited February 2021
    I just touched the 1 inch pipes going to the indirect and they are not hot but warm so there are hot all the time.  I do believe when there’s a call for heat the system seems to work perfectly but the domestic hot water side again empties out.  When the domestic hot water runs out of the indirect the burner does not turn on because it’s happy at about 170°. But again I do believe if there’s a call for  heat the burner does cover that.  That is a picture of the aquastat with the cover off and I’m sorry that wire is covering the temperature but the aquastat is set at 140°.
  • Denniss516
    Denniss516 Member Posts: 35

  • Denniss516
    Denniss516 Member Posts: 35
    I want to add a piece of information that I think I’m overlooking. We got a new oil burner probably 15 years ago and then 10 years ago when gas came in to my area we replaced it with a gas burner. Both those burners had the same indirect storage tank. I’m looking for something that might be defective. However it might be that some thing from the very beginning is the issue. Without the storage tank of course we didn’t have enough hot water at that point the storage tank gives us more but it runs out. Maybe I was barking up the wrong tree. Maybe the problem is from day one. When the oil burner was installed the manager and technician said I’ll have plenty of hot water. The same comment came from the guy who did the gas burner conversion said the same thing in fact I remember him telling me he has three daughters and he never runs out of hot water. I have one wife and I run out. Thanks again
  • JUGHNE
    JUGHNE Member Posts: 9,756
    That looks to be a simple aquastat, switch on or off.
    Someone please reply if otherwise.

    Have you tried to simply turn the temp up all the way and see if boiler fires and pump starts. Return to original position or a little higher is it fired.
    If you move the temp wheel back and forth do you hear a click....the room may have to be quiet?

    If that is the simple switch I think it is, you can put both wires under one screw, shut the power off first, this in effect closes the aquastat and calls for burner and pump. Then turn the power back on and see what happens.
  • PC7060
    PC7060 Member Posts: 709
    edited February 2021
    I do recall warning on the forum (@hot_rod ?) that running higher temps (180F) will cause increased scale build up.
    Feel free to ignore this this relatively uniformed comment, but I found that Level 2 on the Grundfos pump was too high for my DHW circulator on my low head system, mine runs with 10-20F temp drop at L1 speed with low head. Not sure if over-pumping results in scale built up.

    This is a situation where the Grundfos Alpha2 come in handy with the GPM display.

  • HomerJSmith
    HomerJSmith Member Posts: 1,562
    I have a 45 gal HTP indirect which I run at 150 deg with a tempering valve. It also runs on a sensor, not an aquastat with priority mode that switches the boiler to 190 deg water to the indirect. I never run out of hot water.

    Maybe you should be looking at your boiler settings.
  • JUGHNE
    JUGHNE Member Posts: 9,756
    The HTP tank he has does not match up to a HTP boiler.
    So I believe it requires an aquastat (on-off) rather than a sensor that would go to the boiler.
    Someone here may know about how the priority system works with his ES-2 boiler.

    Owner could follow the cable from the tank back to the boiler, look under the cover and see if it mentions a priority setting for DHW.
  • JUGHNE
    JUGHNE Member Posts: 9,756
    After conferring with a supplier, that aquastat is simply just that, a switch.
    If you power down and put both wires under one screw, then power up.
    The boiler should fire (assuming it is shut off-cooled down) and the DHW pump should start.
    You can hear the pump with a screwdriver handle stuck against your ear with the tip on the pump housing.
    If it is pumping the hot will of course be hot and after a few minutes the return pipe should cool down a bit.

    If this does not all function then you have a problem with wiring at the boiler.
  • HomerJSmith
    HomerJSmith Member Posts: 1,562
    Ya, it doesn't look like a mod-con, so probably doesn't have programing. I don't know what kind of boiler it is. His best bet is a tempering valve and higher tank temps, I guess.
  • Denniss516
    Denniss516 Member Posts: 35
    edited February 2021
    I have tried moving the aquastat up and down, thinking it was dirty. I followed wires inside I didn’t see any info other than what the codes mean. I just went down temp on burner showed 130, moved aquastat heard click and burner fired up, circulator is on felt hum. Another question is, if the indirect empties where does it get refilled from, the burner which is 170 degrees? Can it get refilled from a different source? That would make sense why it’s cold and burner stays off at 170 degrees when water gets cold.  The heating system works fine, burner goes on when heat is on and burner temperature drops. Again, thinking outside the box could there be a different issue due to the fact this has been going on for years and years like someone said about gravity?  Thanks again appreciate help. Happy wife happy life would be nice :)
  • mattmia2
    mattmia2 Member Posts: 5,510
    The burner in the boiler will come on when the temperature of the boiler drops from circulating boiler water in the indirect water heater. There is an aquastat on the boiler that controls the burner, the burner won't fire until the indirect has taken enough heat away from the boiler for the temp to drop to the cut in point of the aquastat on the boiler. If the temp doesn't drop on the boiler, the water gets cold in the indirect water heater and the burner in the boiler isn't firing, that would suggest that heating system water is not circulating through the indirect and moving heat from the boiler to the indirect water heater. It could be the rotor in the pump is stuck, it could be the pump isn't getting power, there could be a valve that is shut or a strainer or check valve or other device that is clogged and maybe a few other causes.

    The indirect water heater has a coil in it that a circulator in the heating system circulates heating system water through and that coil acts as a heat exchanger that heats the potable water in the tank in the indirect water heater.
    HomerJSmith
  • JUGHNE
    JUGHNE Member Posts: 9,756
    Just to clarify, the boiler water and your domestic hot water (showers etc) never mix.
    The tank sits there full of water pressurized by your city water. Cold comes in to push the hot up to the shower when you open the valve upstairs.
    The boiler water is in the tube inside the tank, the heat from the boiler water transfers thru the tube heating up your domestic water tank.
    When your domestic water cools down to maybe 110 then the aquastat calls the burner and pump to come on, your boiler water has to be hotter than 110 to heat up the tank, the 170 will heat it up pretty quick as long as the pump is moving the boiler water thru the tube. When the tank water gets up to say 125 or whatever the setting of the aquastat is the boiler should shut down and the pump turn off.

    I wonder if your aquastat was sticking and when you exercised it, it closed its switch to start the boiler.
    The temp of the boiler should not matter as far as what your tank wants. But it has to heat up to perhaps 170 to do it's job. If your boiler was set at 100 degrees the pump would still try to heat your tank. But obviously won't heat the tank above 100 degrees.

    Do you feel any temp difference between the pipe in and pipe out of the BOILER connections to the tank?
    You should feel some drop if the pump is running especially if the tank is cooled.

    If this works correctly you should have very long hot showers.

    What type of heater emitters do you have in the house??


  • Denniss516
    Denniss516 Member Posts: 35
    JUGHNE said:

    Just to clarify, the boiler water and your domestic hot water (showers etc) never mix.
    The tank sits there full of water pressurized by your city water. Cold comes in to push the hot up to the shower when you open the valve upstairs.
    The boiler water is in the tube inside the tank, the heat from the boiler water transfers thru the tube heating up your domestic water tank.
    When your domestic water cools down to maybe 110 then the aquastat calls the burner and pump to come on, your boiler water has to be hotter than 110 to heat up the tank, the 170 will heat it up pretty quick as long as the pump is moving the boiler water thru the tube. When the tank water gets up to say 125 or whatever the setting of the aquastat is the boiler should shut down and the pump turn off.

    I wonder if your aquastat was sticking and when you exercised it, it closed its switch to start the boiler.
    The temp of the boiler should not matter as far as what your tank wants. But it has to heat up to perhaps 170 to do it's job. If your boiler was set at 100 degrees the pump would still try to heat your tank. But obviously won't heat the tank above 100 degrees.

    Do you feel any temp difference between the pipe in and pipe out of the BOILER connections to the tank?
    You should feel some drop if the pump is running especially if the tank is cooled.

    If this works correctly you should have very long hot showers.

    What type of heater emitters do you have in the house??


    One 1 inch pipe comes from the circulator to the indirect and the other 1 inch looks like it goes to the heating system. Both feel the same now just slightly warm. By emitters do you mean baseboard answer is yes.
  • Denniss516
    Denniss516 Member Posts: 35
    mattmia2 said:

    The burner in the boiler will come on when the temperature of the boiler drops from circulating boiler water in the indirect water heater. There is an aquastat on the boiler that controls the burner, the burner won't fire until the indirect has taken enough heat away from the boiler for the temp to drop to the cut in point of the aquastat on the boiler. If the temp doesn't drop on the boiler, the water gets cold in the indirect water heater and the burner in the boiler isn't firing, that would suggest that heating system water is not circulating through the indirect and moving heat from the boiler to the indirect water heater. It could be the rotor in the pump is stuck, it could be the pump isn't getting power, there could be a valve that is shut or a strainer or check valve or other device that is clogged and maybe a few other causes.

    The indirect water heater has a coil in it that a circulator in the heating system circulates heating system water through and that coil acts as a heat exchanger that heats the potable water in the tank in the indirect water heater.


    That is my symptom, however, after maybe 15 minutes we have hot water again. I can't understand why the boiler doesn't turn on when the indirect empties of the hot water. I called the guy who installed my boiler, he says maybe change the "well" and control. Whats a well?
  • HomerJSmith
    HomerJSmith Member Posts: 1,562
    edited February 2021
    I'm going out on a limb, here. What is the street pressure to your house. It should be 55 psi. If you have high house pressure you are going to run out of water a lot faster. You won't really notice it taking a shower if it is 55 psi. The shower is where one gets clean, not for getting a massage.

    If it is too high, you can install a Pressure Reducing Valve. You can get a hose bibb gauge at Home Depot and measure it.

    The loop for the indirect W/H should come off the boiler outlet and into the boiler inlet without flow moving thru the house heating sys. If the boiler doesn't have priority mode, a controller with priority mode may help. So you have house heating or indirect heating not both at the same time.

    Both your Grundfos 15-58 pumps should have check valves in the volute. If one of those two pumps are the indirect pump and the house pump is off and the indirect pump is on, you could be pulling water thru the house volute into the indirect pump tempering the tank supply.
  • Zman
    Zman Member Posts: 7,328
    How many gpm is the shower pulling?
    The easiest way to check this is to turn on the shower and see how long it takes to fill a 5 gallon bucket.


    I think there are 4 possible issues:
    • You have a very high flow shower head and the system simply can't keep up.
    • There is an issue with the aquastat not responding quickly enough.
    • There is an issue involving a lack of check valves and the heating system stealing heat that is supposed to go to the indirect.
    • You have a scaled up coil in the indirect.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Larry WeingartenCanuckerHomerJSmith
  • JUGHNE
    JUGHNE Member Posts: 9,756
    The "well" is usually the term used to describe the insert tube into the tank.
    It has no moving parts..it holds the aquastat bulb/probe in a tunnel/well so it can sense the temp of the tank. Sometimes conductive grease is applied to ensure heat transfer.

    Your service guy may change the aquastat if defective. I would guess he would jumper it out to see if the boiler functions as it should.
    Ask him if the DHW circuit has a priority connection in the boiler.
    He can isolate the DHW circuit with the ball valves that go to the house heat, doing this he can determine if there are check valves in the pump.

    As Homer said above, without the check valves the tank pump can pull water back thru the heater circuits, closing the heater valves temporarily will show that right away.
  • neilc
    neilc Member Posts: 1,804
    are we sure of the circulator ?
    you say it hot on both sides where it mounted at the boiler manifold,
    but is it "boiler hot" going into the bottom of the domestic tank ?
    I think you've said warm and warm at the tank,
    you're not getting circulation to the tank
    known to beat dead horses
  • neilc
    neilc Member Posts: 1,804
    and the 2 posts above me about check valves on the 2 other heating circuits
    known to beat dead horses
  • Denniss516
    Denniss516 Member Posts: 35

  • Denniss516
    Denniss516 Member Posts: 35
    I posted these pictures and my comments earlier yet they did not appear so I’ll try again. As my wife went to the shower this morning I went downstairs and watched and felt the pipes and the temperature. As the temperature went down on the boiler it fired up and went back up to 170°. I felt and listened with a screwdriver to the circulator pumps and two were on. I ran upstairs and shut off the heat. Then I heard just one of the circulator pumps on that go to the indirect tank. Both 1 inch pipes and the output for domestic hot water were all extremely hot. I thought everything was working perfectly. I went upstairs and asked my wife how the water in the shower was and she said she had a keep on turning up the hot water more and more when I felt the water coming out of the shower it was not hot any longer. I ran downstairs the temperature gage did show 170° and the domestic coming out of the tank was slightly warm both 1 inch pipes were still extremely hot. The only noise I heard was water going through the storage tank. 
  • Denniss516
    Denniss516 Member Posts: 35
    I forgot to mention one more thing. I did move the aquastat from 100 to 160 I heard no clicking. I’m assuming that are already was on. Is it OK for me the next time to jump out the two terminals without shutting off the burner? To see what happens at that point. Thank you again
  • JUGHNE
    JUGHNE Member Posts: 9,756
    The reason to shut off the power while you move one wire to place both under one screw (jumping that switch in the aquastat) is so you do not accidently ground the 24 volt circuit. After you have both wires under one screw then you can turn the power back on. If all is good in the boiler control wiring and devices, the boiler should fire, if not already up too max temp, and the pump for DHW should start.

    If that happens then you shut off the heat at the thermostats upstairs.
    If you then shut off the ball valves for the heat to upstairs you isolate the boiler, DHW pump and the tank from everything else.
    The very hot boiler water should go into the tank and somewhat cooler water return to the boiler.
    Have you identified the domestic hot and cold pipes from the boiler in and out pipes?
    Feel the temp of boiler pipes right at the tank in and out.
    If you run some hot out of the shower valve then you may feel more of a temp difference on boiler in/out pipes.
  • Denniss516
    Denniss516 Member Posts: 35
    JUGHNE said:

    The reason to shut off the power while you move one wire to place both under one screw (jumping that switch in the aquastat) is so you do not accidently ground the 24 volt circuit. After you have both wires under one screw then you can turn the power back on. If all is good in the boiler control wiring and devices, the boiler should fire, if not already up too max temp, and the pump for DHW should start.

    If that happens then you shut off the heat at the thermostats upstairs.
    If you then shut off the ball valves for the heat to upstairs you isolate the boiler, DHW pump and the tank from everything else.
    The very hot boiler water should go into the tank and somewhat cooler water return to the boiler.
    Have you identified the domestic hot and cold pipes from the boiler in and out pipes?
    Feel the temp of boiler pipes right at the tank in and out.
    If you run some hot out of the shower valve then you may feel more of a temp difference on boiler in/out pipes.

    Thank you !! I ordered an Aquastat today, just to rule out that. A local Plumber here wants $250 first hour and $150 each add'l. Not that I don't want to pay him for his expertise, not sure he will figure it out and throw out 400. So I want to at least rule the aquastat out for $60. easy to change. BTW, I wasn't going to remove a wire and put both wires together I was going to use a jumper wire. I assume the aquastat is a normally open circuit, when the temp goes below temp set, it closes the circuit. Question, when jumping out the aquastat, I should hear the circulator go on, no matter what else is happening, correct? I am still wondering if something else could be wrong. Water pressure (not checked) I feel is fine, I have plenty of force. i will do your test. Thanks again !! Dennis
  • mattmia2
    mattmia2 Member Posts: 5,510
    A relay somewhere should turn on the circulator with the call from the aquastat. The aquastat itself only running low energy control would be low on my list of suspects. Where does the flex that goes to the circulators go?

    Also, no prices, especially for labor.
  • Denniss516
    Denniss516 Member Posts: 35
    mattmia2 said:
    A relay somewhere should turn on the circulator with the call from the aquastat. The aquastat itself only running low energy control would be low on my list of suspects. Where does the flex that goes to the circulators go? Also, no prices, especially for labor.
    Sorry flex? The reason I chose the aquastat first is because it is about 15 years old. Also it’s reasonable priced for replacement. And I felt that was a good place to start. I could be wrong but I wanted to start somewhere.
  • mattmia2
    mattmia2 Member Posts: 5,510
    Do you have a multimeter? That would be where I would start. You should measure 24vac across the aquastat when it is off(open) and 0 vac when it is on(closed).

    Flex-flexible metalic conduit or in that case it might be metallic cable, but in any case, it is the line voltage wiring that goes to the circulators.
  • HomerJSmith
    HomerJSmith Member Posts: 1,562
    edited February 2021
    Replacing the aquastat is fine, it's cheap and you can do it. I wouldn't set the aquastat higher than 125 deg if you don't have a tempering valve on the tank. A 45 gal tank doesn't last long if you have long showers unless the boiler can adjust the supply temp upwards for the indirect. I set my boilers that have indirect priority temperature at 190 degs.

    What is the water quality coming from the street main? Hard water can affect the transfer of heat across the HX. 1mm of a layer of minerals on a HX can reduce heat energy transfer about 12%, as I remember. What is the street pressure?