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Need to Adjust Expansion Tank Pressure If I Adjust House PRV?

D107
D107 Member Posts: 1,799
edited June 2019 in Gas Heating
For some reason boiler pressure, set at 16, went from 16 to 22 a few weeks ago. Reverse indirect pressure also now even higher. I know I could drain a little water from the indirect tank and/or the heating system and see if pressure stabilizes. However in looking for the cause, I checked house pressure which years ago was 60; now measures 71, 4 below the house PRV limit. Could be increase in street pressure or an issue with the 13 year old Watts PRV. I would like to back street pressure down to 60 or even 50 and see if that effects boiler pressure. But I don't want to do it if that will effect the expansion tank in a negative way or require it to be adjusted immediately which I'm not qualified to do.

I know there could be various causes of the increased pressure. The exp tank sounds hollow only on the very top when I tap it, but I have a feeling the Hydroclaw might muffle the sound a bit.

Comments

  • Ironman
    Ironman Member Posts: 6,868
    The cold static fill pressure (fill valve setting) should be a minimum of 12 psi for single story; 15 psi for a two story; and 18 psi for a three story house.

    The air pressure in the expansion tank should be set to match the fill valve setting. This is with NO water pressure on the tank which means it needs to be isolated from the system when adjusting the air pressure.

    If the air pressure in the tank doesn't match the cold static fill pressure, then the capacity of the expansion tank is reduced.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    D107
  • hot_rod
    hot_rod Member Posts: 16,309
    Does the boiler fill valve have a shut off valve upstream? If so fill the boiler cold, to say 16 psi and shut the valve off. Be sure the tank was recharged to 16 psi also, you may need to drain the system down or remove the tank to check that.
    Any increase in pressure will be from thermal expansion. Really as longs you stay below the pressure relief valve setting, typically 30 psi, you should be fine.

    16- 22 is not a concern. Excessive increase could indicate the pre-charge in the tank was not accurate (16 psi) the tank is undersized.

    As far as the house pressure, plumbing codes indicate 15 psi min, limit of 80 psi. Most house pressure reducing valves are factory pre-set at 45 psi.

    If the main line has a back flow or check valve you need a domestic water thermal expansion tank also.

    The boiler fill valve should be rated to 150 psi or more, Caleffi are rated to 230 psi max. inlet pressure.

    Generally speaking you should not exceed a 3:1 ratio on a pressure reducing valve, some manufacturers suggest 2:1.
    Use a two step regulator if you need to make a large pressure reduction.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    D107
  • HVACNUT
    HVACNUT Member Posts: 4,594
    If the boiler PRV is functioning properly then the domestic pressure shouldn't effect boiler pressure at all. Unless of course theres a crack or hole in the reverse indirect HX.
    Its possible the boiler PRV is bypassing.
    D107
  • D107
    D107 Member Posts: 1,799
    I had another thread on part of this last month, having to do with the sizing of the exp tank. Based on this online sizer, https://westank.com/calculator/ it appears installer sized it correctly (Extrol #30); I just can't account for, after two months, a sudden increase from 16 to 22 in pressure reading at the feed, and a reading from the Turbomax tank of 32--though it must be off since there's been no relief valve weeping yet. I'm limited in what I can do myself.
  • D107
    D107 Member Posts: 1,799
    I could probably test the turbomax pressure myself by screwing my gauge to the bottom drain threads. Having great time at dentist so this will have to wait.
  • hot_rod
    hot_rod Member Posts: 16,309
    D107 said:

    I had another thread on part of this last month, having to do with the sizing of the exp tank. Based on this online sizer, https://westank.com/calculator/ it appears installer sized it correctly (Extrol #30); I just can't account for, after two months, a sudden increase from 16 to 22 in pressure reading at the feed, and a reading from the Turbomax tank of 32--though it must be off since there's been no relief valve weeping yet. I'm limited in what I can do myself.

    Being a reverse indirect, I assume you keep it hot all the time, and at a set temperature?

    If the temperature of the tank swings, certainly the pressure will increase as the tank gets warmer. So pressure will vary depending on when you are looking at it.

    If it never exceeds 22- 25 psi i would not be concerned.

    Keep in mind when you run higher fill pressure, and adjust the tank pre-charge to a higher psi, you limit the expansion tanks acceptance capacity.

    Some of the tank sizer software programs allow you to enter that info, cold fill pressure for example, and high temperature and pressure at highest temperature. assuming you have total volume guessed or calculated accurately.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    D107
  • D107
    D107 Member Posts: 1,799
    @Ironman Based on the measured height of our heating system, cold static fill pressure would be 16.5psi, which matches the fill valve setting.

    @hot_rod Yes, our Caleffi 553 fill valve has max working pressure of 230psi and pressure setting range 0 to 60. We do have shutoff valve upstream. Yes we keep turbomax cut in at 140, cut out 150. Less concerned with boiler 20-22 psi--though I'd like to know why it suddenly went up 6psi--but the turbomax 32psi is a concern though since no relief valve weeping probably gauge is off. I just went to look at turbomax drain valve and I see it's a yellow gas ball valve with a gate valve after it. Wouldn't the smaller orifice of a valve for gas not be so useful as a drain valve where you want volume? Anyway I could gauge the turbomax psi by screwing my pressure gauge onto that gate valve threads.

    If I'm only getting a hollow sound from the very top of the exp tank that sounds a little off unless the tight fit of the hydro class is muting that sound.

    I have seen this testing advised online: "you want to check to see if the PRV is not faulty. bring the pressure down to where is needed for your system--presumably by draining a little water-- then shut off the feed to the boiler; if the pressure still rises then it's not your PRV its something else."


  • hot_rod
    hot_rod Member Posts: 16,309
    Does your fill valve have a pressure gauge? if not there should be a taped hole to add on. Get an accurate gauge on the system first.

    Also the grey knob on the bottom of the 553 is a shutoff valve. Turn it counterclockwise like any wheeled valve to shut off any flow 100%

    I still suspect the pressure gauge on theTurboMax is not accurate? Unless you confirm that with a new gauge, it is just guessing.

    The tank could see a higher pressure if it sees the delta P developed by the circulator. Check all pressures with no circulators running to get "static" pressure readings.

    Yes adding a test gauge to a drain cock would be quick and easy.

    The tank holds boiler water, so you should not need to flush sediment out, but a full port ball valve is a faster way to drain.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • D107
    D107 Member Posts: 1,799
    edited June 2019
    @Hotrod Good news is Turbomax drain cock reads 22psi, same as gauge on 553. So Turbomax gauge is off--assuming pressure is same or less near the top than at the drain cock. That's with burner off, no circs running a few hours after last dhw call. PSI runs between 20-22 making DHW. We can see in winter if that swings higher with the heating added. Turbomax gauge should be replaceable on warranty. Lowered house water pressure from 70 to 60--no effect on boiler system pressure but just better for us overall.