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Pressure drop with hot water demand

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2

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  • mattmia2
    mattmia2 Member Posts: 9,740
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    Maybe the outlet of the boiler side of the reverse indirect is plugged. Does the circulator for the dhw zone pump in to the tank? Maybe the water is pushed in to the tank but can't get out. does the pressure immediatly spring back up if you turn off the circulator?

  • mattmia2
    mattmia2 Member Posts: 9,740
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    What doed the pressure gauge on the reverse indirect say when the system pressure drops? Is the auto air vent on the reverse indirect working? Is the cap loose so it can vent?

  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited March 2023
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    I'm confused. Does the arrow on the volute point right (red arrow) or left (green arrow).

    It looks like the green arrow.

    I would have mounted the pump on the intake to the TurboMax rather than the return to the boiler. I always pump in to the highest pressure loss which is the input to the coil. Since the pump is on the return to the boiler, I would put a spring check valve in the red box on the following photo and program the boiler for water heater priority. And I would have a spring check in the volute of that red Grundfos pump. Perhaps all those pumps should have a spring check in the volutes?

  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited March 2023
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    Since the TurboMax doesn't have an aquastat, I wonder how the TurboMax tells the boiler what the temperature in the tank is.

    What happens if you have 15 psi pushing in one direction and 12 psi pushing against it from the other direction? What would the boiler pressure gauge read? I'm talking dynamic flow. Just wondering.

  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited March 2023
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    Just for fun, what if you closed one yellow handled ball valve on the boiler pump, one on the distribution pump and one on the distribution return and turned on the W/H pump. What would the pressure reading on the boiler gauge read? What would be the reading if all valves are opened and only the W/H pump was operating?

  • Palisandr
    Palisandr Member Posts: 30
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    I meant to say that we do not use the temperature control unit, which came with turbomax, temperature gauge from Turbomax is directly plugged into the TT board.

  • Jamie Hall
    Jamie Hall Member Posts: 23,430
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    you will get flow from the 15 psi direction towards the directio with 12 psi. The flow rate will be such as to absorb the 3 psi differential in the length of pipe and fitting between the two pressure gauges as a friction loss. The gauge readins won't be altered.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HomerJSmith
    HomerJSmith Member Posts: 2,468
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    Jamie, I will tell you what I was thinking. If the indirect pump is putting out 15 psi and the flow is going to the boiler return and at the same time the flow was going thru the boiler pump in reverse and HX (the path with the greater pressure loss) and these two pressures meet at the gauge that it might be like a differential pressure meter and register the pressure differential.

    Thanks for the reply.

  • hot_rod
    hot_rod Member Posts: 22,254
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    the indirect is a reverse type, the boiler water is in the tank, pressure drop should be just the piping and fittings.

    To me it looks like it is pumping away.

    There is a restrictor disc in some of those reverse Indirects, the ErgoMax has them, but it is on the cold inlet to the tank

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Palisandr
    Palisandr Member Posts: 30
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    I feel that owe an update to the group.

    So, after closing/opening the Caleffi PRV system is stable at ~20 psi with LWCO sensor connected normally in the boiler.

    Looks like the opening/closing/opening cycles of the PRV removed some kind of obstruction. When I closed/opened it first time during the system pressure drop I definitely heard the gush of water and the system pressurized to ~17psi - the one specified on the Caleffi dial. Still not sure if that was the culprit, but I've ordered the newer model with the manometer on it and will replace the old one.

    Thank you all for trying and helping to solve the problem.

  • Alan (California Radiant) Forbes
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    Well, that would be a first. I asked that you turn off the fill valve to see if the pressure stayed at zero after the event as that would indicate a leak.

    So, pressure goes to zero on a DHW call and then recovers. How can a fill valve do this?

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    HomerJSmith
  • mattmia2
    mattmia2 Member Posts: 9,740
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    Trapped air.

    HomerJSmith
  • mattmia2
    mattmia2 Member Posts: 9,740
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    @HomerJSmith I don't think we know what the gauge on the reverse indirect says (or if it actually has one). My thought is that with the prv stuck as the system pressure dropped some air collected in the reverse inderect and the circulator is pumping in to that tank of ware with air over it and compressing the air so the pressure on the suction side of the cirusulator drops while the pressure in the reverse indirect increases.

  • dko
    dko Member Posts: 611
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    @mattmia2 he says the pressure gauge on the indirect matches the readings of the boiler gauge. The gauge on the indirect reads the pressure in its tank (system).

    This just seems like a thing where you have to be there in person to start hearing, seeing, and noticing all the little happenings around the system to find out exactly what is going on. I'm sure if one of you were over there you'd have figured it out within the hour.

    @Palisandr are you saying you no longer lose pressure when using the hot water?

    hot_rod
  • mattmia2
    mattmia2 Member Posts: 9,740
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    It has to be going somewhere and compressing a pocket of air somewhere or a huge leak are pretty much your only options and the circumstances for the leak would be weird.

  • ttekushan_3
    ttekushan_3 Member Posts: 958
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    forgive me if I missed it, but is there a pressure reducing valve on the water main into the house.

    Having the boiler feed PRV replenishing again to mask a short circuit that may even have been plumbed in erroneously during installation is no comfort.

    terry
  • Palisandr
    Palisandr Member Posts: 30
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    1. initial state: Caleffi valve completely closed, pressure is at 17.5 psi. LWCO sensor connected as normal in TT.
    2. opened a hot water faucet in the tub upstairs, pressure started to drop quite fast, down to ~0 in a span of a minute. Boiler threw b26 error (LWCO sensor). Hot water still flows in the tub with normal pressure, but became brownish.
    3. Closed the tub faucet, bypassed LWCO sensor on the boiler (b26 error dissapeared), boiler called for hot water, pressure building up. All these with the Caleffi valve comletely closed. After the hot water heating cycle finished the system pressure was up to 19 psi.

    I think I should get a really good plumber to figure out my system (guys who installed through my general contractor were not very good, they don't exist as a company anymore). I tend to agree with ttekushan_3 that the system itself is not optimally plumbed and the stuck PRV caused the problem (which I understand it should not and may be it did not).

    Anybody can recommend a knowledgeable professional in the Denver area? Seems that most of the people on this forum are from the East and searching for a pro in Denver using forum's "search for contractor tool" does not yield a single name.

    Thanks.

  • hot_rod
    hot_rod Member Posts: 22,254
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    Advanced Hydronics in Denver is one of the best. Been doing Hydronics since 1989

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited March 2023
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    Palisandr, I asked you to close some valve and look at the pressure gauges while the call for heat in the TurboMax. Why don't you do that. I want to see what the pressure gauges read when every thing is shut off except the TurboMax heating circuit and the running H/W pump. I'm betting that the pressure remains high without a decrease in pressure. I really want to verify my thoughts on what I think is happening.

    Why anyone would think that the Caleffi pressure regulating valve would be the problem in a dynamic operating sys with sys pressure irregularities is beyond me.

    We know that with all the valves open and only the Hot/Water pump running that there are pressure irregularities.

  • Jamie Hall
    Jamie Hall Member Posts: 23,430
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    I'd still like to know how a change in flow or pressure on the heating side of the system can effect the pressure on the domestic hot water side, oor vice versa without there being an hydraulic connection between the two.

    Maybe I'm a little slow or something, but what I read from the OP in a nutshell is that if he runs the domestic hot water the pressure on the heating side goes to zero and he sometimes gets brown water on the domestic side.

    Frankly, I think that there is more than one thing wrong here — at the very least very low or poor domestic water pressure and at least one faulty valve — but I have yet to see a diagram of the system, nor some key pressure and flow measurements.

    What I do see, if the symptoms which I outlined above are correct, is a potential rather severe health hazard.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Larry Weingartenttekushan_3SuperTechHomerJSmith
  • Alan (California Radiant) Forbes
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    I think I should get a really good plumber to figure out my system


    Perhaps, but this is a tough one. Try to find a sole proprietor that only does hydronics with at least 20 years in the trenches.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • mattmia2
    mattmia2 Member Posts: 9,740
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    I don't see the mystery — other than your domestic water static presure is low. If you open a hot water tap upstairs, and the pressuren on the heating side of the boiler drops… you have a leak between the boiler and the hot water. Either a baclflow nfrom the boiler fill to the hot water line (you mentioned the backflow preventer vent drips? if so, it needs repair or replacement) or in the Turbomax coils. Those are the only two hydraulic connections. All the electric stuff is irrelevant to the pressure problem.

    It is easy enough to see if there is a leak between the system and the dhw. Turn off the cold water supply to the reverse indirect, leave the make up water to the boiler on and open a hot water faucet. there should be no flow, if there is either the hx in the reverse indirect is leaking or the valve isn't holding.
    Solid_Fuel_Man
  • dko
    dko Member Posts: 611
    edited March 2023
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    His system with lines that I drew while thinking few days ago but then he said it was working again so :o :

    ttekushan_3HomerJSmithAlan (California Radiant) ForbesPalisandr
  • Jamie Hall
    Jamie Hall Member Posts: 23,430
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    mattmia2 said:

    I don't see the mystery — other than your domestic water static presure is low. If you open a hot water tap upstairs, and the pressuren on the heating side of the boiler drops… you have a leak between the boiler and the hot water. Either a baclflow nfrom the boiler fill to the hot water line (you mentioned the backflow preventer vent drips? if so, it needs repair or replacement) or in the Turbomax coils. Those are the only two hydraulic connections. All the electric stuff is irrelevant to the pressure problem.

    It is easy enough to see if there is a leak between the system and the dhw. Turn off the cold water supply to the reverse indirect, leave the make up water to the boiler on and open a hot water faucet. there should be no flow, if there is either the hx in the reverse indirect is leaking or the valve isn't holding.
    True. Has that been done? Did I miss the test somewhere in the fog up there?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 9,740
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    I think this is the first we asked. they may need to add a valve for that.
  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited March 2023
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    mattmia2, if there was a leak in the heat exchanger in the TurboMax, boiler pressure would rise to street pressure, don't you think? Highest pressure wins.
    dko, I like what you did. I never do my closely spaced tees this way. I have them on the boiler loop not on the distribution loop. I count the present configuration a mistake. I count the W/H pump pumping into the boiler HX a mistake. Pump into the TurboMax, the highest pressure loss. There needs to be a check valve on the TurboMax pump and a check valve on the black boiler pump. This is elementary.

    Yahoo, we got a spell check, thanks Erin. Now I won't look so dumb. They say actions speak louder than words, tho.

    Back to the discussion. Even the distribution pump need a check valve for a possible thermo siphon problem.

    This sys has 2 boiler pumps, the black one and the Grundfos W/H pump. In priority mode, the Grundfos pump is the boiler pump, pumping 150-190 deg water into the TurboMax. In space heating mode, the black boiler pump is moving water thru the boiler HX to be pumped into the distribution sys which appears to be an ECM (?) pump.

    There is no water loss from the sys. "All these with the Caleffi valve completely closed. After the hot water heating cycle finished the system pressure was up to 19 psi." I'm guessing the air charge on the EX-tank is the same as the Caleffi fill valve pressure setting.

    I think the brown domestic water is another problem and not related to the pressure irregularities. Maybe he has domestic iron piping?

    I look at the pressure irregularities as a piping problem pending further review.

  • mattmia2
    mattmia2 Member Posts: 9,740
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    mattmia2, if there was a leak in the heat exchanger in the TurboMax, boiler pressure would rise to street pressure, don't you think?

    Usually. Maybe not depending on things like domestic water supply pressure, check valves, or tempering valves. Since it is a huge health hazard and it isn't clear what is happening it should be tested.
  • Jamie Hall
    Jamie Hall Member Posts: 23,430
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    "if there was a leak in the heat exchanger in the TurboMax, boiler pressure would rise to street pressure, don't you think"

    You are making the completely unwarranted assumption that the "street pressure" is higher. If this is a private well, it may not be at times. For that matter, in some public systems it may not be at times.

    One of the first rules of diagniostics is to look at the simplest solutions first. As I understand the OP's problem -- and please correct me if I am wrong -- at least at times when there is a domestic hot water demand in his system the pressure in the heating system drops, sometimes to zero. Unless I am mistaken, there is no way to do that without there being a hydraulic connection between the two.

    Find it and fix it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ttekushan_3
  • mattmia2
    mattmia2 Member Posts: 9,740
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    Does it happen as soon as a tap is opened or does it happen on the dhw call?
  • hot_rod
    hot_rod Member Posts: 22,254
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    mattmia2, if there was a leak in the heat exchanger in the TurboMax, boiler pressure would rise to street pressure, don't you think? Highest pressure wins.
    dko, I like what you did. I never do my closely spaced tees this way. I have them on the boiler loop not on the distribution loop. I count the present configuration a mistake. I count the W/H pump pumping into the boiler HX a mistake. Pump into the TurboMax, the highest pressure loss. There needs to be a check valve on the TurboMax pump and a check valve on the black boiler pump. This is elementary.

    Yahoo, we got a spell check, thanks Erin. Now I won't look so dumb. They say actions speak louder than words, tho.

    Back to the discussion. Even the distribution pump need a check valve for a possible thermo siphon problem.

    This sys has 2 boiler pumps, the black one and the Grundfos W/H pump. In priority mode, the Grundfos pump is the boiler pump, pumping 150-190 deg water into the TurboMax. In space heating mode, the black boiler pump is moving water thru the boiler HX to be pumped into the distribution sys which appears to be an ECM (?) pump.

    There is no water loss from the sys. "All these with the Caleffi valve completely closed. After the hot water heating cycle finished the system pressure was up to 19 psi." I'm guessing the air charge on the EX-tank is the same as the Caleffi fill valve pressure setting.

    I think the brown domestic water is another problem and not related to the pressure irregularities. Maybe he has domestic iron piping?

    I look at the pressure irregularities as a piping problem pending further review.

    Here is a pic of a reverse indirect, there is virtually no pressure drop in the tank, pumping in to that fire tube should not be a problem with a small 15-58.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited April 2023
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    mattmia2, tested, yes. I discussed a tempering valve and possible lockup because of calcification, but I'm not sure Palisandr has a tempering valve even tho TurboMax shows one on their installation diagram.

    jamie, "when there is a domestic hot water demand in his system the pressure in the heating system drops, sometimes to zero. Unless I am mistaken, there is no way to do that without there being a hydraulic connection between the two." Bingo. Not on a well. Ya, when you see hoof prints, think horses not zebras. Ya, pressure drops when there is a call for hot water (TuboMax). I have never seen street pressure as low as 17.5 psi (19 psi hot).

    Yes, the pressure drop in the TurboMax tank is non existent, but there is other head energy lowering piping in that circuit. So, the Grundfos pump is pumping into a low loss fire tube HX into the EX-tank. Hmmm.

    Some how one must account for the pressure irregularities and I haven't seen anything that qualifies.
    I've stated what I think is going on, nothing I have asks for has been done to verify whether I'm right or barking up the wrong tree.

    Good discussion!
  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited March 2023
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    I sure and Hell hope Palisandr tells us what the problem was and how it was fixed. I have too much time invested in this post. Enquiring minds want to know.
    Solid_Fuel_Man
  • dko
    dko Member Posts: 611
    edited April 2023
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    I sure and Hell hope Palisandr tells us what the problem was and how it was fixed. I have too much time invested in this post. Enquiring minds want to know.

    He did, I just ended up with more questions than answers.
    He said his system is now working fine after he fiddled with the fill valve.
    It just started working again.

    I surely stopped thinking about it as there are too many unknown variables.
    HomerJSmith
  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited April 2023
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    dko, that's not my interpretation.

    1. initial state: Caleffi valve completely closed, pressure is at 17.5 psi. LWCO sensor connected as normal in TT.
    2. opened a hot water faucet in the tub upstairs, pressure started to drop quite fast, down to ~0 in a span of a minute. Boiler threw b26 error (LWCO sensor). Hot water still flows in the tub with normal pressure, but became brownish.
    3.Closed the tub faucet, bypassed LWCO sensor on the boiler (b26 error dissapeared), boiler called for hot water, pressure building up. All these with the Caleffi valve comletely closed. After the hot water heating cycle finished the system pressure was up to 19 psi.

    I think I should get a really good plumber to figure out my system (guys who installed through my general contractor were not very good, they don't exist as a company anymore). I tend to agree with ttekushan_3 that the system itself is not optimally plumbed and the stuck PRV caused the problem (which I understand it should not and may be it did not).
  • dko
    dko Member Posts: 611
    edited April 2023
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    I asked a couple times for confirmation if it was working now and was never answered, but I suppose there were many other posts to respond to.

    "So, after closing/opening the Caleffi PRV system is stable at ~20 psi with LWCO sensor connected normally in the boiler.
    Looks like the opening/closing/opening cycles of the PRV removed some kind of obstruction."

    To me, your quote above ("stuck PRV caused the problem" past tense) and this quote seems to read that his system now works and assumes the PRV was the culprit. As he has not attempted or inquired about the next steps to try. And possibly wants a really good plumber to figure out the system once it does become a problem again?

    Could be wrong, guess we'll know when he responds.

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,044
    edited April 2023
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    I think there's a vacuum developing in the Turbomax.

    Maybe it wasn't seen before because the pressure reducing valve was working and refilling the system when the pressure dropped. And then when the system cooled down and the pressure increased, the relief valve would open.

    Once the pressure reducing valve stopped working, the pressure dropped and the LWCO opened, turning off the boiler.

    @Gsmith turned the light on in my head in one of his comments on the @ethicalpaul thread, "Equalizer disabled experiment video". Even though the topic was steam, I've had this zero pressure thread on my mind.

    https://forum.heatinghelp.com/discussion/192055/equalizer-disabled-experiment-video/p1
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    I think there was just enough water in the closed loop to keep the pressure up with no makeup water. EX tank either water logged or over aired. When domestic water was run the temp drop in the TurboMax made the water contract, which was on the teetering edge of pressure with no air cushion and no makeup water pressure dropped. Closed system....

    Now with makeup water working pressure back up and we can assume EX tank is taking the expanded volume, or else the relief valve would be dripping during a call for heat. 

    That's my take.....
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    HomerJSmithttekushan_3
  • Palisandr
    Palisandr Member Posts: 30
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    Update: Turned out to be a faulty Turbomax tank. Swapped Turbomax t109 with a Viessman Vitocell 300-V (300L) and the closed PRV does not show any pressure drop in the system on hot water demand. Turbomax seemed to work much less than a 40-year promise by the manufacturer.
    Solid_Fuel_Man
  • Jamie Hall
    Jamie Hall Member Posts: 23,430
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    Thanks for the update -- that was a puzzler!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England