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Use Tekmar reset control with MZ boiler?

pch Member Posts: 2
I am a DIYer. Twenty years ago we purchased a home built in 1898. In the 50s it was turned into 4 apartments, then not much was changed until we started to turn in back into a single-family home.

Prior to our second winter in the house, I removed the ancient, inefficient, 50-year-old beast of a furnace and its ducting, and installed a Monitor MZ 25 (which ran on propane that year. I didn't update the gas service until the following summer). For the past 18 years the MZ has faithfully provided hot water and single high-temp zone heat, supplying a fan coil (SpacePak) in the attic. I am now in the process of installing radiant floor heat on the first floor, old houses can be a bit drafty, which will require a second temperature zone.

Eventually I will need a new boiler, but would like to put that off for now.

OK, large preamble, here comes the question... It's a two-parter.
1. I know that MPI came out with a boiler reset control a couple of years after we installed, but we did not need it because of the single heating zone. The addition of the in-floor heat changes that. I have a Tekmar 422 Reset control. Can that be used in place of the Monitor reset control? How? Specifically, the control wiring: the MPI reset comes with a wiring harness, I have not seen anything in the MZ manual related to connecting a reset. Maybe my manual is too old?
2. Since, at some point, I will need to replace the MZ, I would like to set up the system so that I can swap in the new boiler without making (major) changes.

Thanks for any help.


  • Ironman
    Ironman Member Posts: 7,076
    edited November 2022
    I’m not familiar with that particular boiler, but any control strategy MUST have a matching piping strategy.

    We frequency use injection mixing with a Tekmar 356 when two separate SWTs are required. And that will generally work with any type of boiler. I think that the 422 functions similarly. You can also use a smart mixing valve, but again, the piping will have to be made to match the controls.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 18,224
    It was, is a basic on off boiler, one of the very first condenser, not much control logic. A MZ still operating has to be a very rare case :)

    Your next boiler may come with all the control functions, so might not be a good investment to buy a stand alone tekmar?

    If you need two temperatures a 3 way valve would be the least expensive option, requiring some piping changes.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • pch
    pch Member Posts: 2
    I gather from the comments that the MZ does not respond to reset commands? I am a bit confused. What then does the MPI 9110 MZ OUTDOOR RESET CONTROL do?

    As for piping, I believe I have a reasonable plan for that. I will install a 30g Boiler Buddy to provide hydraulic separation and some mass to help limit short-cycling. I also will install a 3-way valve with a circulator for the in-floor zone. I was hoping that I could get a lower boiler temp when only the in-floor calls for heat and therefor a bit more efficiency.

    Thanks for the comments!
  • hot_rod
    hot_rod Member Posts: 18,224
    Sounds like you have the optional module. Which, to me, looks suspiciously like a tekmar component :)

    Are you piped primary secondary? I think you need that to get a two temperature system.

    Know when you direct pipe the boiler needs 3.5- 4 gpm minimum. So a small zone may not be workable without primary secondary.

    The manual has some suggested multi temperature piping options.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,508
    edited November 2022
    Surprisingly, we have 3, maybe 4 still going; parts are still available. They were all installed in 2000. If I had one, I’d be replacing it next summer. 

    High temperature systems lasted longer as the condensate from radiant systems eventually compromised the HX. 

    Don’t throw a lot of money for ODR on your new radiant. Maybe just a 3-way mixing valve. And you may have to tie it into an existing zone to keep the flow rate high enough to keep the boiler happy. 
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour