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Low flow in closed in floor heating system

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ASnatchA
ASnatchA Member Posts: 30


Having issues with my in floor heating system not circulating enough flow.

It started with a ignition error on my boiler and I replaced the ignitors and the boilers been running since. The problem is it runs for a while but it kicks out after about 30 minutes to an hour on low flow. Boiler stops, circulation pump keeps running. The boilers only showing 0.5 - 0.8 gal / min flow.

There's a Grundfos 15-58FC circulation pump that appears to be running well. I magnetic rotation checked it and it looked good. I pulled the motor and took a look at the impellor and everything looked normal and spun freely.

I've cycled purged the system thinking I had a bunch of air in the system but no air came out and didn't take any more glycol. Systems running at 13 psi but still kicks out.

Even when the system runs it doesn't feel like it's putting much heat into the floor. I can feel warmth where the pipes start but never gets very far and the return pipe stays cold.

I was thinking of replacing the Grundfos pump but I don't see anything wrong with it.

Any ideas what I can check next?

Thanks
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Comments

  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    I think low flow means low flow thru the boiler. Does the boiler loop have it's own circ?
    Also, did it ever work properly?

    There was an error rendering this rich post.

  • ASnatchA
    ASnatchA Member Posts: 30
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    Yes low flow through the boiler. There's a flow readout that shows 0.8ish and will drop down to 0.5 gal/min and then the boiler will shut off. I didn't think it had it's own circ.

    System was working well before although I kinda thought it was taking a long time to heat the building.
  • neilc
    neilc Member Posts: 2,708
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    that's not a boiler,
    it's a water heater,
    wrong application,
    it needs street or well pressure to drive flow thru it,

    it does have an option to add recirculation for a domestic system, not sure how it woll react when hotter heating water returns to it though.

    wrong application
    known to beat dead horses
    Mad Dog_2
  • ASnatchA
    ASnatchA Member Posts: 30
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    Yeah sorry, people keep calling it a boiler when I talk to them but yes it's just a on demand water heater. It's been running fine in this application for 10 years.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,806
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    It is a tankless water heater being used as a boiler . Is there a manifold for the radiant loops ? What speed is the circulator set to ?

    There was an error rendering this rich post.

  • neilc
    neilc Member Posts: 2,708
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    ok, it worked before,
    there's only this one circulator?
    anything else changed?
    picture at manifolds,
    and tubing type?
    known to beat dead horses
  • GroundUp
    GroundUp Member Posts: 1,926
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    It's piped wrong and is the wrong appliance for the job. A larger pump would help the flow issue, but the only way to actually fix it is to start over with the correct appliance and piping arrangement.
    Mad Dog_2
  • neilc
    neilc Member Posts: 2,708
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    does that WH have an inlet water filter?
    is it clean?
    pg39
    known to beat dead horses
    Mad Dog_2
  • ASnatchA
    ASnatchA Member Posts: 30
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    Sorry I'll take a pic when I get back home. It's got 3 zones with no isolation valves on them.

    Yes just the one circulation pump. 

    Nothing else changed that I can think of.
  • ASnatchA
    ASnatchA Member Posts: 30
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    No inlet water filter. I opened it and nothing was installed.
  • neilc
    neilc Member Posts: 2,708
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    that might be good, or bad,
    flush / reverse flush the heating coil,
    known to beat dead horses
    Mad Dog_2
  • ASnatchA
    ASnatchA Member Posts: 30
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    I did a normal flush already but I'll try both because why not. Let you know how it goes. 
  • ASnatchA
    ASnatchA Member Posts: 30
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    So I flushed it both ways and then fired it up and watched the flow closely.

    Starts up at 1.8 gal/min for about 5 minutes then the heater sounds like it kicked up and then the flow started dropping. Dropped all the way down to 0.3 gal/min over the next 10 minutes and then shut itself off.

    I ordered the replacement ignition parts when the ignition failed and cleaned the ones that were in it and put them back in. Seemed to work but maybe they still have issues??? I don't know but the parts get here tomorrow so I'll swap them out and see if that helps.

    I'll keep you posted.
  • neilc
    neilc Member Posts: 2,708
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    are you able to determine a return water temp to the WH,
    I bet that what's shutting you down
    known to beat dead horses
  • hot_rod
    hot_rod Member Posts: 22,262
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    What type of radiant tubing is it connected to?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ASnatchA
    ASnatchA Member Posts: 30
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    Not sure. Can you tell from this pic?



    Return water temperature is generally cold and stays pretty cold. I'm going to bring home my FLIR from work and see where the heats going.

  • neilc
    neilc Member Posts: 2,708
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    how about a closeup on that 3rd tube on top, where the printing is
    known to beat dead horses
  • ASnatchA
    ASnatchA Member Posts: 30
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  • ASnatchA
    ASnatchA Member Posts: 30
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    Well changed the ignitors with the new parts and nothing changed. Same thing. Started with flow and dropped shortly after it started up until it stopped.

    llinesLooking at the floor with a thermal gun really only showed one like that was slightly warmer. Maybe the lines are plugged but doesn't explain why I can circulate with an external pump no problem.

    Not urgent as I have backup electrical heat but still more confused then anything. On the waitlist for the contractor that installed it so guess I'll wait unless anyone has any ideas.

  • hot_rod
    hot_rod Member Posts: 22,262
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    did you power up the circulator when you had it removed? You need to know it actually spins when powered. The magnetic indicators do not necessarily indicate rotation.


    what powers the circulator, maybe that is the issue?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ASnatchA
    ASnatchA Member Posts: 30
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    No, I didn't power it up when I had it out. That would have been good to rule out. Going to make a list of things to check when I drain and charge the system again.

    I found that if I close the CW or HW valve while its running the flow drops to 0, heater turns off and then I open it again the flow jumps right back up.

    Also this noise is happening now at the circulator I didn't notice before. The But only when the flow is higher. Lower its quiet.

    https://drive.google.com/file/d/13MyDGB6BZ6psdmTuQ89YsQZ8xqc2jMja/view?usp=drivesdk

    HeHeeH MaybetMaybeebyaM

  • ASnatchA
    ASnatchA Member Posts: 30
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    No I didn't power it up when I had it removed. That would have been good to eliminate.

    Check out this sound I noticed thecirculator making. It's pretty quiet so I have my phone right up to it.

    https://youtube.com/shorts/6YBnjTbryEU?feature=share

  • Dave Carpentier
    Dave Carpentier Member Posts: 595
    edited March 2023
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    Would the unit show flow rate during the flushing ?

    How about the air vent ? Could the body be gunked ?

    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • hot_rod
    hot_rod Member Posts: 22,262
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    Yes, the easiest component to check for blockage would be the air purger at the high point

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ASnatchA
    ASnatchA Member Posts: 30
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    Okay I'll open that up and take a look tomorrow. I'll open the ciculator and see how it runs out. Anything else I should check while I have the system bled?

  • hot_rod
    hot_rod Member Posts: 22,262
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    has it always worked with that 15-58?


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ASnatchA
    ASnatchA Member Posts: 30
    edited March 2023
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    No, I didn't power the circulator up when I had it removed. Would have been good to rule that out.

    I notice that as the pressure drops if I close the HW or CW valve, the pressure drops to 0, unit shuts off and when I open it back up the full flow is back again. I don't know if that's anything or not.

    I also noticed the circulator making this sound when it is running and the heater reads a high flow (1.8 gal / min). It stops making the sound when the flow drops off.

    https://drive.google.com/file/d/13MyDGB6BZ6psdmTuQ89YsQZ8xqc2jMja/view?usp=share_link

    Not sure if you can view that file or not. Let me know if it's clear.

  • ASnatchA
    ASnatchA Member Posts: 30
    edited March 2023
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    Sorry, posted that comment yesterday but didn't post. It's the same sound as before.

    And yes. It's always worked with the 15-58. Tag says it was installed in 2015.

  • ASnatchA
    ASnatchA Member Posts: 30
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    Well I think I have it down to there is something in my Rinnai that is restricting the flow as it runs for whatever reason.

    I ran it with the external pump and circulating through and it started restricting flow for whatever reason. I'm narrowing into the Bypass control device or the Water flow control device. Suspecting for whatever reason the water flow control device is closing off as it runs. Starting to do some research into why today so if anyone has any suggestions, I'd apprieciate it.

    Thanks guys.

  • hot_rod
    hot_rod Member Posts: 22,262
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    Did you try Rinnai tech support? Or the local rep? They usually know the most common failures.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ASnatchA
    ASnatchA Member Posts: 30
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    helpThe service tech showed up today and didn't know much. He tried calling tech support and they weren't too impressed with the use of the on demand system and didn't help him. Told me it's not really worth it for him to troubleshoot without there help and I agree. I'll try myself tomorrow.

    In the meantime I found some nice troubleshooting manuals that I'm going to pick through.

  • davidd
    davidd Member Posts: 84
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    Is it possible that it has a heat sensor that has gone bad? If it has the ability to restrict flow so that it can keep the output at a fixed temperature, maybe the output temperature sensor thinks it is colder than it truly is. Alternatively, if it uses a flow measuring mechanism, maybe that thinks the water flow is faster than it really is. Alternatively, if the output temperature or flow are adjustable, maybe that adjustment mechanism has been adjusted up or down, respectively?

  • EternalNoob
    EternalNoob Member Posts: 42
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    in addition to / independent of the above advise, my understanding of the rule of thumb for using an on-demand WH (rather than boiler) is to use primary and secondary pumping, with a flat-plate heat exchanger rather than close tees.

    As others have pointed out, the ODWH is notably not a boiler and ideally wants higher pressure and higher flow to function. This means it might work ok when first installed, but then the slightest bit of corrosion/rust/buildup, some of which is inevitable in a radiant system, will quickly inhibit the pre-filter of an ODWH and dramatically restrict flow. Buildup will be mitigated with a primary loop isolated by a FPHE, and a pump dedicated to pushing water through the WH while the other radiant pump puts the heat into the floor, will share the pumping work.

    Also, running your system at higher pressure than the standard / typical 12-15 psi of most radiant systems is advised. Check the specs of the WH to see if it has a minimum operating pressure. It might want minimum 30 psi.

  • ASnatchA
    ASnatchA Member Posts: 30
    edited March 2023
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    That is super interesting and pretty much matches the results what I saw last night.

    Update! - So I gave it a good flush with vinegar, through the heater loop, then with water, then I put the glycol back in the heater. Then I gave it a long cycle through the floor tubes and filtered the glycol with a 5um bag filter. Flushed and backflushed the heater through the filter. And brought the system pressure up to 20psi.

    It ran good overnight! Maintainted flow at 2.2 gal / min. Not sure what is ideal but looking at the pump curves I thought this was on the lower end for the 15-58. It's running on high.

    The thing is the fine filter in the system was never really overwhelmed with material. The bag filter that I filtered the glycol had a fair bit of debris in it. I'm thinking the main issue is something in the boiler has got plugged and builds up as it runs until it starts restricting flow. Because even when I was doing a flush with the external 0.5 hp pump it started restricting at first. I might look for a cleaner designed for them and give it a really good clean. Any recommendations?

    Anyways I can't really believe that the flush got it working again. Now I don't get to take apart the inlet water control devise and bypass. 😕 . Might do it anyways. ha.

  • Dave Carpentier
    Dave Carpentier Member Posts: 595
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    How much glycol do you have in the system ?

    A glycol mix is good for freeze protection, but it's 'thicker' than straight water.

    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • ASnatchA
    ASnatchA Member Posts: 30
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    It's 50% glycol. Well I'm very much assuming that as its pretty much the standard in cold climates like where I live.

  • GroundUp
    GroundUp Member Posts: 1,926
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    50% is never necessary unless it'll reach actual fluid temp of -40F. 30-35% is normal for radiant systems in even the coldest of climates

  • neilc
    neilc Member Posts: 2,708
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    maybe that circulator is getting tired of pushing against the WH,

    and or is there a capacitor on the motor and is it to spec?

    known to beat dead horses
  • hot_rod
    hot_rod Member Posts: 22,262
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    First question, do you really need glycol? Any exposed piping, is the home left unattended in below freezing conditions?

    If yes, what temperature protection is needed?

    There is a freeze point, starts turning to slush, and a burst point where it can freeze solid and break things.

    If glycol is optional I'd look at burst temperature. 35% should cover most locations.

    36% Dowfrost get you to a -40F burst, about a 5°F freeze (slush forming)

    Look at the info on the glycol you are considering, the protection temperatures vary. Some of the low cost, diluted glycols have less protection range.

    Dow does a good job of explaining the selection criteria.

    A freeze alert device may be a better investment, gets you plumbing and heating protection notification. I put a remote wireless temperature sensor under my kitchen sink. The Ecobee thermostat notifies on my phone me if it triggers.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream