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JPL941
JPL941 Member Posts: 51
edited August 2023 in Gas Heating
Hello

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,916
    The pressure relief valve is not an option. If you don't have one on there, you're way out of code. Furthermore, it must be located between the hot water outlet (port 2) and any valve or other flow restriction.

    In most cases, when the installation instructions use the word "must" (see the notice in the diagram you provided), they mean "must" -- so I have to admit I fail to see what the question is?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    edited April 2020
    OK tell me if I understand your query.
    You turn on cold water (not hot water) faucet in the house and the combi boiler is activated to operate as if it was a call for hot water.
    Is that right?

    Assuming that is correct... there is a flow switch in most tankless water heaters. Many of these switches are some type of propeller that moves faster as the flow increases. This change in speed sends a signal to the CPU (computer geek-speak) to tell the gas valve how much gas is needed. Faster means more water so you need more gas to heat the water. Slower means less gas to heat the water .

    Now, you have a 40-gallon tank (this defeats the purpose of the tankless water heater by the way) with an air cushion expansion tank. As the water heats and cools in the system this air cushion takes up the slack. As water temperature increases it expands and needs a place to go. This tank is where it goes. As the water cools, the air pressure in the tank pushes the expanded water out as it shrinks.

    That said, when you open a faucet any water in the air cushion tank will be released. This pressure change may be rapid and cause a momentary acceleration of the water past the tankless water heater flow control. The flow may be back and forth like a spring bouncing back and forth, but only for a few seconds.


    The location of the air cushion tank might be the answer to your problem. Place it on the cold water pipe before the Vega distribution block.

    Just a thought...
    if you leave the tank in the same location then change the check valve location to the place in the boiler instructions

    Pick one or the other, not both. check valve only needed if the tank is in the hot water line. It MUST be used if the tank is in the hot water line.

    Next question. When did the problem start?
    A. Always had problem
    B. After I installed the vega distribution block
    C. After we replaced / installed / repaired the (Xxxxxxx)

    You need to think like Sherlock H2Olmes
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • JPL941
    JPL941 Member Posts: 51
    edited August 2023
    Y
  • Jamie Hall
    Jamie Hall Member Posts: 22,916
    I'm sorry. I must be missing something quite essential. What, exactly, is the problem with piping that poor thing the way the manufacturer says you should?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HVACNUT
    HVACNUT Member Posts: 5,744
    Could single lever faucets cause that?
  • Jamie Hall
    Jamie Hall Member Posts: 22,916
    HVACNUT said:

    Could single lever faucets cause that?

    Easily, if they aren't completely on the cold side when operated.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    OK Somewhere in your home this is happening. A hot water branch and a cold water branch are connected together, then after the connection, there's a valve that is closed. This can be on a washing machine or a shower valve or appliance that has a need for mixed warm (hot and cold mixed) water.
    Maybe, if you wash your car with warm water, you have one of these.


    If you can't think of anything like that, then use the process of elimination. Close each hot water branch one at a time. Then test your system to see if the problem goes away.

    If that does not locate the problem, then try the cold water branches one at a time. If that does not locate the problem then the cross over is between the un-valved main hot and cold connections at the top (in the picture)

    You really do need to solve it. Every false start is another real start cycle on the components causing wear and tear on the components of the tankless water heater.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • JPL941
    JPL941 Member Posts: 51
    edited August 2023

    I

  • Jamie Hall
    Jamie Hall Member Posts: 22,916

    I'm sorry. I must be missing something quite essential. What, exactly, is the problem with piping that poor thing the way the manufacturer says you should?

    OK, so I'll post it again. Look at the control device labelled 4 in the manufacturer's Figure 43 and just do it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JPL941
    JPL941 Member Posts: 51
    edited August 2023


  • Jamie Hall
    Jamie Hall Member Posts: 22,916
    Then it is a draw on the hot water line somewhere, somehow. Close valve 6. Then the phantom flow can't happen -- in either direction. Then track down the location of the phantom flow -- as has been mentioned, it may be a single handle faucet anywhere in the house.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JPL941
    JPL941 Member Posts: 51
    edited August 2023

    I

  • hot_rod
    hot_rod Member Posts: 21,853
    Add a pressure gauge near the heater. Buy one with an indicator hand and see if you get pressure fluctuations. 80 psi is the most pressure you want, plumbing codes indicate 25- 89 psi
    A regulator and thermal expansion tank may be needed?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • BillyO
    BillyO Member Posts: 277
    I have never used this manifold before but is there a chance its faulty? just looking for most obvious first
  • JPL941
    JPL941 Member Posts: 51
    edited August 2023

    Hello