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munchkin piping problems

helgy_2 Member Posts: 14
Recently our company installed a muchkin 80m as a replacement boiler. Along with an indirect water heater and two zones of floor heat. This is on top of the existing two zone high temp fin tube. I have it set up as primary secondary pumping. With heat traps on all runs that go to the floors above the boiler. Well whats happening is when the indirect water heater calls for operation the fin tube zones will migrate heat through them as well even though there pumps are not running. I piped the whole system using the close T's method for pulling off my secondary zones. Any ideas, please let me know. If you need more info I can sure get it...

Thanks, Helgy


  • hot_rod
    hot_rod Member Posts: 21,874
    Not sure what you

    mean by heat traps? The thermal drop legs help but I have had to go back on a couple and add checks. I feel they need to be more like 2-3 feet deep to protect, sometimes:)

    If you take your secondary tees off the top side of the primary loop, this almost always encourages ghost flows. The hotter more bouyant water will always travel up.

    Droping down from the bottom side of the PS loop, thermal drop, then up helps. Sometimes, however it requires checks on both S&R lines from the primary loop to completly handle the ghost. You can actually have a small two way travel of heat. Hot water rising and cooler water falling in the same pipe!

    I've switched to check pumps for this type of installation, but still a second spring or flow check may be needed, to prevent the two way flow I mentioned.

    Hard to know which ones will need additional flow check protection. I've found short primary loops through boilers requiring high head pumps seem to be the worst offenders.

    I understand the PS theory and math, but sometimes, somehow, on some systems, you get the problem. It often shows as overheated indirect tanks, as a small flow when other zones call will allow the indirect tank to run up to boiler temperature! Might be wise to add a scald guard type of thermostatic mixer on the DHW.

    For the cost difference I have found the check pump, and additional check valve on the return leg are wotth installing on the initial piping. Much cheaper than a drain, cut, solder, and repipe.

    This link give you some more info.


    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TGO_21
    TGO_21 Member Posts: 1
    sounds like

    ghost flow. In addition to the thermal traps and close tees you may need to put in flow check valves. Dan has written about this in the past, it may be in hot tech topics. Hope this helps.
  • Darin Cook_2
    Darin Cook_2 Member Posts: 205
    Munchy Piping

    Helgy, You really did not need to use pri/sec piping on the 80 since you are probably using a 007 or like pump. You will need to add flow checks to the supply,return, or both since the heat traps are not stopping gravity flow. A good style pump to use in the future is one with the integral flow check. They make for a faster,easier install. Making heat traps is okay but it is one of those things that may or may not work and it sometimes does not work with no real clear reason why. Sometimes even with one flow check it will not stop gravity flow. If in doubt contact HTP they will be more than willing to help you.
  • Ted_5
    Ted_5 Member Posts: 272
    Next time Vitodens!

    look into the Viessmann Vitodens. Another set of tappings off the boiler to go to DHW tank. No P/S needed, in fact you are better off on a condencing boiler not to! You want the coldest water coming back, not bypassing the hotest water to the boiler. The 2 smaller boilers come with a veriable speed pump built in and that is the DHW production pump. Check it out!

  • Steve Ebels
    Steve Ebels Member Posts: 904
    Most indirects

    Require a pretty good flow and your indirect pump is likely larger than your primary loop pump flow-wise. It's pulling more water off the primary loop than the primary loop itself is flowing. This can make for all sorts of wierd flows and stuff. the simplest solution is to install flow checks on all the loops.
  • Einsiedler
    Einsiedler Member Posts: 61

    I like to lockout P1 (primary pump) when Indirect Pump is on. (Ensures priority to DHW)

    If the primary is still on during DHW call, weird flows will happen

  • munchkin-man
    munchkin-man Member Posts: 247

    Please send me a drawing of how you have the piping so I can take a look at it and offer you some addvice. I had someone send me a drawing simular to what you are discribing with thermal loops, and I recomended a flow check on the return side to prevent ghost flow and a mixing devise on the hot out let of the indirect as a precaution. The indirect should be piped from the supply and return of the heater at the heater supply and return. This helps prevents ghost flow through the indirect The use of a spring check is the best way to go so that as each zone is energized it will open that zone spring check only. Other plunger type flow checks can open when an oposit zone is energized if the zone being energized has a circulator larger than the rest or has the ability to push large amounts of water for what ever reason. Like a high head/volocity type. It is common to use circulators with built in checks and I have used many and found they are effective. Both Grunfos and Taco make pumps with internal checks. I have used both and so far have not had any problems. I will be back in the office on the 15th. Send your drawing to 508-763-3769 attention Jeff Cook / Rick Sousa jr./ Guy Wilard. One of my Technicians will contact me and go over it with me so I can get you an answer to you before the 14th.
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