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Lowering pressure (gas boiler)?

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northernsoul
northernsoul Member Posts: 134
Hi there

I have an 18 year old slant fin boiler connected to original 1930s cast iron system. I had the auto feeder valve replaced in the summer (low pressure) but now the cold pressure reads at 20 (I’m in a 2 story house) and it was creeping up to 23/24 when I turned on the heat.

I think that is too high - so how can I lower it safely back to around 12-15? The fill valve is now set at 15 (the tech left it at 20 when they filled it back up )

Can I do that just by bleeding some rads? Or do I have to also bleed the old expansion tank ?

Thanks - we’ve hit cold season so in a small panic

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  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    Did the tech empty the expansion tank when he replaced the auto feed, and why was that changed?
    First locate the valve before the feeder, and shut it off. Shut off the boiler. Then let enough water out of the expansion tank drain to empty it. Knocking on the side of the tank should enable you to tell when most of the water has drained out Close the tank valve, and open the feed valve. This will reestablish the air cushion in the tank, compensating for the expansion of the system water as it heats up. Turn on the boiler.
    Keep a daily watch on the pressure, in case the pressure rises again. Does the system make hot water as well?—NBC
  • delta T
    delta T Member Posts: 884
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    Shut off the water supply, drain some water out of the drain on the boiler (or any other convenient spot in the system) until the pressure is at 12 - 15 psi, turn the water back on and make sure it doesn't creep up slowly over time.
  • northernsoul
    northernsoul Member Posts: 134
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    > @delta T said:
    > Shut off the water supply, drain some water out of the drain on the boiler (or any other convenient spot in the system) until the pressure is at 12 - 15 psi, turn the water back on and make sure it doesn't creep up slowly over time.

    Can I let water out at a rad by bleeding it, or should it be a drain on the expansion tank/boiler?

    Thanks !
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    You may be draining several gallons out, and draining the tank will make sure that it is not waterlogged.—NBC
    delta T
  • northernsoul
    northernsoul Member Posts: 134
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    > @nicholas bonham-carter said:
    > Did the tech empty the expansion tank when he replaced the auto feed, and why was that changed?
    > First locate the valve before the feeder, and shut it off. Shut off the boiler. Then let enough water out of the expansion tank drain to empty it. Knocking on the side of the tank should enable you to tell when most of the water has drained out Close the tank valve, and open the feed valve. This will reestablish the air cushion in the tank, compensating for the expansion of the system water as it heats up. Turn on the boiler.
    > Keep a daily watch on the pressure, in case the pressure rises again. Does the system make hot water as well?—NBC

    Would I need to empty the tank completely or just enough water to get the dial back to show 15?

    Thanks !> @nicholas bonham-carter said:
    > You may be draining several gallons out, and draining the tank will make sure that it is not waterlogged.—NBC

    Okay so drain out enough until the pressure drops enough . Gotcha thanks
  • northernsoul
    northernsoul Member Posts: 134
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    > @northernsoul said:
    > > @nicholas bonham-carter said:
    > > Did the tech empty the expansion tank when he replaced the auto feed, and why was that changed?

    Yes they emptied the tank when they drained the system. I am guessing they charged it back up too high to 20.

    Auto feed was replaced as it was old and not filling back the system and pressure was stuck around 10 and didn’t heat all the upstairs rads
  • northernsoul
    northernsoul Member Posts: 134
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    > @nicholas bonham-carter said:
    > Did the tech empty the expansion tank when he replaced the auto feed, and why was that changed?
    > First locate the valve before the feeder, and shut it off. Shut off the boiler. Then let enough water out of the expansion tank drain to empty it. Knocking on the side of the tank should enable you to tell when most of the water has drained out Close the tank valve, and open the feed valve. This will reestablish the air cushion in the tank, compensating for the expansion of the system water as it heats up. Turn on the boiler.
    > Keep a daily watch on the pressure, in case the pressure rises again. Does the system make hot water as well?—NBC

    Is this the tap I turn to drain the expansion tank?

    Thanks
  • northernsoul
    northernsoul Member Posts: 134
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    > @nicholas bonham-carter said:
    > You may be draining several gallons out, and draining the tank will make sure that it is not waterlogged.—NBC

    Thanks for your help. Connected a hose to the tank and drained it empty. Opened all the valves back open and it went to my preset level of 15 cold. Ran the boiler at at full heat it went up to 20. So seems to be working well.

    Will keep an eye on it for s few days
  • DZoro
    DZoro Member Posts: 1,048
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    Did the tech change anything else, like add a air elimination device? Hope not, just asking. Could you post a big picture of the system? Just curious.
  • northernsoul
    northernsoul Member Posts: 134
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    > @DZoro said:
    > Did the tech change anything else, like add a air elimination device? Hope not, just asking. Could you post a big picture of the system? Just curious.

    They replaced the auto feeder, and put in a new water supply shutoff. No other upgrades or mods

    Are you thinking there might be another issue ?

    I’ll take a pic
  • HVACNUT
    HVACNUT Member Posts: 5,857
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    > @northernsoul said:
    > > @DZoro said:
    > > Did the tech change anything else, like add a air elimination device? Hope not, just asking. Could you post a big picture of the system? Just curious.
    >
    > They replaced the auto feeder, and put in a new water supply shutoff. No other upgrades or mods
    >
    > Are you thinking there might be another issue ?
    >
    > I’ll take a pic

    Any automatic air eliminator on an air control system (an expansion tank vs. extrol diaphragm) is not proper, even on the rads. Manual blenders on the rads.

    Is there a tankless coil for domestic hot water?
    Was the auto feed replaced because of creeping pressure?
  • northernsoul
    northernsoul Member Posts: 134
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    > @HVACNUT said:
    > > @northernsoul said:
    > > > @DZoro said:
    > > > Did the tech change anything else, like add a air elimination device? Hope not, just asking. Could you post a big picture of the system? Just curious.
    > >
    > > They replaced the auto feeder, and put in a new water supply shutoff. No other upgrades or mods
    > >
    > > Are you thinking there might be another issue ?
    > >
    > > I’ll take a pic
    >
    > Any automatic air eliminator on an air control system (an expansion tank vs. extrol diaphragm) is not proper, even on the rads. Manual blenders on the rads.
    >
    > Is there a tankless coil for domestic hot water?
    > Was the auto feed replaced because of creeping pressure?

    The hot water tank is a separate machine / not tied in.
    Auto feed was replaced as it was not keeping pressure high enough and the turn knob was faulty
  • HVACNUT
    HVACNUT Member Posts: 5,857
    edited October 2018
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    I dont know why the tech adjusted the setting on the new PRV. Factory set at 12 psi specifically for a 2 story house with the boiler in the basement.

    If you drained the X tank like nicholas bonham-carter said, and the pressure stays at or below 20 psi at limit, it should be good. 12 to 15 better, but ok.

    I dont understand why guys mess with things that dont need messing with.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    If the tank is full, then the pressure will rise enough to drip out the pressure relief valve as the water heats up, and expands in volume. If the tank is empty, then the pressure will stay constant hot or cold.
    Draining the tank will ensure that there is an air cushion to absorb the water volume expansion as it heats up.—NBC
  • northernsoul
    northernsoul Member Posts: 134
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    > @nicholas bonham-carter said:
    > If the tank is full, then the pressure will rise enough to drip out the pressure relief valve as the water heats up, and expands in volume. If the tank is empty, then the pressure will stay constant hot or cold.
    > Draining the tank will ensure that there is an air cushion to absorb the water volume expansion as it heats up.—NBC

    It was I’m guessing around half full at least - if drained out for a while. The oressure Now goes from about 15 cold to 20 hot. Better than 20 and 25 etc