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Odd Pressure problem in my boiler

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by nate379, Nov 3, 2011.

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  1. nate379

    nate379 Guest

    This is a natural gas boiler, but that doesn't really matter.

    A couple weeks back I drained down teh system to install a small water-air Modine heater in my garage. My house and garage are slab heat. I put in the Modine to help with warming up the garage faster.

    Anyway, I refilled the system, purged the air and all seemed ok. A few days latter I check on everything and my boiler pressure was pushing close to 30psi! Normally it sits around 15psi. I bled some water off and seemed to be ok. Also turned the regulator down a couple turns.

    Few hours later go check on it and the regulator is pissing out water.

    I thought maybe it failed, but know I have it turned off and the pressure is going from 0psi when the boiler is cold to 20psi when it's warm. I have never had that kind of change before.

    The only other thing I did was add more air to the expansion tank. It only had about 5psi in it. The info I was told is it should be system pressure + 2-3psi. I filled it to 18psi.

    Any ideas on what is going on?

    I'm going to replace the regulator because it's leaking, but the pressure issue has me confused. Should I let air out of the expansion tank?

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  2. North of 60

    North of 60 Minister of Fire

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    Nate, your expansion tank pressure should be checked at atmosphere if you didn't. No system influence. The pressure ,if your acceptance volume is sized right should be a couple of psi less than your system pressure. This allows for transfer when it cools down and heats up. Otherwise no transfer until your system pressure is greater than your tank charge. This is what causes pressure fluctuations.
  3. nate379

    nate379 Guest

    Yes I checked it with it unscrewed from the piping. Sounds like maybe I got bad info and put too much air in. This is saying 12psi:
    http://homerepair.about.com/od/heatingcoolingrepair/ss/boier_exp_tank_3.htm

    Something I HATE is my boiler temp/pressure guage is hard to read. The pressure goes to 75psi and only really stars at . The T&P would let off at 30psi, so why would I even need a guage that high? I tried to replace it with a lower one but I haven't been able to find one.
  4. PassionForFire&Water

    PassionForFire&Water Minister of Fire

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    What is the pressure of the city water or your well water system?
    Do you have a fill valve with backflow preventer?
    What's the seeting of the fill valve?
  5. peakbagger

    peakbagger Minister of Fire

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    Regulators get old and usually when they fail is when you are filling up the boiler after a major repair, as it has to open up full which cracks the diaphram inside. Even worse is if you use the fast fill feature of the regulator by flipping the lever, if the regulator is old, its at least a 50/50 chance that the diaphram failed. When the diaphram fails the regulator body usually leaks externally so it sounds like a regulator is the first thing to do.

    There should be a backflow preventer between the boiler and the regulator, if the regulator failed because the boiler pressure was higher than the household pressure, it means the backflow preventer is not working which is bad as it means you have a potential water contamination issue. If you dont have one, its highly recomended that you install one.

    Did you add significant water volume to the system when you added the Modine? If you did, you may have exceeded the capacity of the expansion tank and may have to add another or go for a larger one.
  6. Fred61

    Fred61 Minister of Fire

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    You did too many things at once. Lets say that all those actions were not analytical. Just draining down the boiler would not have caused all the components to fail. The first thing you should have done was shut off the make-up water valve and monitor the operation of the unit. (it shouldn't be on all the time anyway) Once you find that it is or is not the problem then proceed to the next component you suspect might be causing the problem. Now you're down in the muck with everything out of adjustment.
  7. nate379

    nate379 Guest

    Yeah there is a backflow preventor installed to code. It goes water main, backflow, regulator, boiler.

    Regulator was set to 12psi. I didn't mess with the fast flow. I just turned the water on, opened a vent valve on a high point in the piping and let it fill. I have drained and refilled the boiler probably 1/2 a dozen times in the last few years and it's never given me trouble.

    The regulator is about 3 years old.

    It's all good, I'm going to drop the pressure in the expansion tank and go from there.
  8. Countryboy1966

    Countryboy1966 Member

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    Why does a boiler have run at a lower pressure as opposed to say 30psi from standard water pressure?

    I've been running 30psi last three years and have not noticed a thing unless I'm missing something.

    Going back through my system now so I can add a regulator if needed.

    Thanks!
  9. nate379

    nate379 Guest

    Most boilers have a 30psi T&P valve, so 30psi would be not good at all. I would hope your T&P is letting off some pressure? Either that or your pressure guage is off?

    Higher pressure is hard on all the parts. Nothing in a residential system is designed to run with much pressure. 10-12psi is standard.

    Anyhow I got it fixed. I found my digital pressure guage and 18psi on the other gauge I used was almost 30 psi on the digital guage. Dropped the expansion tank to 12psi, tore apart the fill regulator and all seems to be fine. Holding at 12psi now.
  10. North of 60

    North of 60 Minister of Fire

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    T&P stands for temperature and pressure. Used on DHW. Should only be a pressure relief on the boiler side. Residential fittings are still the same as commercial. Pumps etc all same pressure rating. What designates the system pressure is the rating plate on the boiler and pressure vessel's in the system. Taller buildings will require a higher system pressure to allow for circulation at the highest points.
    .433 pounds per ft of head. I round it up to .5 to overcome the differential created across the pump.
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