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oil fired steam boiler (old system) with tankless hot water coil but NO temp. mixing valve

PeteA
PeteA Member Posts: 171
Background: I got a call my sister that her steam boiler (burnham V-33 steam) was stuck ON and had to be shut down via the emergency switch on the wall. I found the original mechanical relay contact was welded/stuck and I was able to fix it temporarily and then swapped the controller to the more modern R7284U. Everything seems to be working great.
But while I was there I noticed the boiler ran quite a long time when the thermostat was not calling for heat so I investigated and found the hot water coil Honeywell aquastat was set to 180 degrees, so it was actually calling for the heat to bring the water back up to temp. I went to her basement faucet and the hot water as I suspected was outrageously hot, there is NO mixing valve in her system at all and someones idea of a gate valve being used as a tempering valve was not even being used since the valve is completely closed. Long story short I need to install a thermostatic temp valve ASAP and could use a little help choosing one. Its a really small house so the pipe runs are very short. There's 3/4 copper entering and leaving nearby the coil so I can cut one in. I just wanted to know if there are any go to reliable set and forget (minimal) maintenance everyone prefers. She has NYC water so mineral content is not an issue in regards to scaling or conditioning of the domestic water.



Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    AM101 with unions for easy maintenance.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    MikeAmann
  • PeteA
    PeteA Member Posts: 171
    thanks Ed I will look it up and see who has it in stock
  • Waher
    Waher Member Posts: 234
    While you're at the boiler, it looks like pressuretrol may be set too high too. Hard to see from the small photo.
    PeteAGrallert
  • PeteA
    PeteA Member Posts: 171
    edited February 2023
    I looked everwhere for the setup manuals for the V-33 so I could verify her settings and make sure everything is right. What is the typical setting for the pressuretrol? Also isn't that huge gauge a little ridiculous for a system that is supposed to operate at a relatively low pressure. Should I swap that for something with smaller increments?
  • PeteA
    PeteA Member Posts: 171
    Waher I just found a great article for setting up the pressuretrol right here on the site. I'll use this as a guide to see what the settings are currently on this boiler. Thanks again

    https://heatinghelp.com/systems-help-center/how-to-set-a-pressuretrol/
    WaherMikeAmann
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    PeteA said:

    thanks Ed I will look it up and see who has it in stock

    I got called away before I could finish. Here is a piping desigh that will also make maintenance easy for you. every 3 years or so you should flush the tankless water heater with a vinegar based cleaning agent. If you have not had it flushed for over 5 years you may need something stronger like Sizzle


    Valve with threaded unions
    https://www.supplyhouse.com/Resideo-Braukmann-AM101-UT-1LF-3-4-NPT-Union-Mixing-Valve-Lead-Free. It is also available with copper sweat or copper press fittings. Califfi also has the same devices https://www.supplyhouse.com/Caleffi-521509A-3-4-Sweat-Connection-MixingCal-3-Way-Thermostatic-Mixing-Valve,

    this is the kit you need to do the flush if you do not already have a water pump. https://www.supplyhouse.com/Rectorseal-68711-Calci-Free-Tankless-Water-Heater-Flush-Kit?_br_psugg_q=tankless+flush+kit If you already have such a pump like for removing water from a swimming pool cover or a water transfer pump of some other type, then all you need is the chemical flush, and a couple of short hoses to connect to the valve #4 in the diagram.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    PeteAMikeAmann
  • PeteA
    PeteA Member Posts: 171
    Ed that's awesome!! Thanks for the piping diagram. I already order the mixer and most of the parts. I secured a propress and I'll probably knock this out this weekend for her once I secure the few additional pieces I see in your drawing.. Really appreciate the extra info
    EdTheHeaterMan
  • CLamb
    CLamb Member Posts: 259
    @EdTheHeaterMan What is the pressure setting of that relief valve?
  • HVACNUT
    HVACNUT Member Posts: 5,744
    edited March 2023
    CLamb said:
    @EdTheHeaterMan What is the pressure setting of that relief valve?
    Most are 150 psi.
    EdTheHeaterManCLamb
  • Jamie Hall
    Jamie Hall Member Posts: 22,916
    On the pressuretrol and gauge -- the pressuretrol should be set to cut in just above 0.5 psi, and cut out 1 psi higher. The big gauge is, as you note, pretty useless -- but it is a requirement (code requires at least one gauge capable of reading twice the safety relief valve pressure). No harm, however, to adding a low pressure gauge somewhere, to see what's really happening.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    PeteA
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,317
    Is it no longer necessary to drop the mixing valve 12" below the coil? That't the way it was always done. Maybe it is not required with the newer valves.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    CLamb said:

    @EdTheHeaterMan What is the pressure setting of that relief valve?

    That can also be a Pressure and Temperature relief valve at 150 PSI and 210°F with a short temperature probe.


    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • PeteA
    PeteA Member Posts: 171
    thanks @Jamie Hall the pressurtrol is actually the next thing I'm going to test and set or replace for her. I took a closer look when I was installing the thermostatic mixing valve and it looked like the pressurtrol was set at 5, way too high for such a small house. I am not sure who worked on this boiler in the past for her but my goal is to get it tuned properly so that it continues to run safely and efficiently for her. This thing must be costing her a fortune to run. I also noticed the venting on her steam mains don't seem to be closing properly also so I'll be replacing those also.