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How Do I Purge my Hydronic Heating System?????

JoeyJoey Posts: 3Member
I have a gas furnace and 2 zones for hydronic heat. I can hear a little gurgling in the pipes and I'm sure there is air somewhere in the system. Question is: How exactly do I purge each zone? Click the link below or copy and paste it for a sketch of my system, that might make describing easier. Basically, in order to purge each zone, which valves do I need to shut off and which stay on.

How long do I run the water through the system? After its all said and done, what pressure should I put the system back up to.

Sorry for all the questions, I appreciate any help!



  • chrischris Posts: 84Member
    purge system

    Your system was installed with future service in mind. Lots of isolation valves are good!!
    For zone 1>
    1.Close valve 5
    2.Open valve 1
    3.use the quick fill on the feed valve #1.
    4.Watch the pressure guage. Keep between 15-20 lbs.
    5.Continue until air stops coming out of the hose.
    6.Close quick fill, close valve 1 make sure pressure is between 10-12lbs. if not bleed off more water through valve 1.
    7.Open valve 5 and your done.

    Repeat for zone 2.
    using valves 4 and 2.

    Good luck.
  • Kal RowKal Row Posts: 1,518Member ✭✭

    -1- shut boiler

    -2- shut valves 4 and 5,

    -3- hook up a hose to bib above #4

    -4- if your boiler's water feed pressure regulator has a lever, lift it straight up to pressurize the system but keep it below 25psi or the boiler's pressure relief valve will open - you might need to play with this lever up and down as you purge, remember the original pressure - the correct pressure cold is the highest point in the system - minus the lowest point in the system in ft divided by 2.33 + 5 - that should be your cold static pressure - eg if you system is 18ft tall, typical 2 story house - from boiler in basement to radiators at floor of level 2, then , 18ft / 2.33 = 7.7, + 5 = 12.7. “12.5” just happens to be the factory setting for most feed regulators, as well as the air pre-charge pressure, on expansion tanks
    - the 2.33ft is because every 28inches of height is 1 lb of pressure, the +5 is to keep at least 5psi of pressure at the highest point to keep the pump from sucking in air

    -5- open bib above #4 and drain on until water runs clear and quiet

    -6- close bib and repeat for bib above #5

    -7- drop feed bypass lever and drain any bib to bring pressure down to orginal level

    -8- reopen valves 4 and 5

    -9- restart boiler and have a nice day

    For more detailed info – you will have to buy dan holohans books and really learn about the systems
  • JoeyJoey Posts: 3Member

    Thanks so much your you help guys!! Quick question...does it matter if I shut both valves 4 and 5 at the same time to drain either zone? Or should I shut 5 and open bib 1, let it drain. Then open 5 shut bib 1. And lastly, shut 4 and open bib 2?
  • chrischris Posts: 84Member

    You can shut them both together. Remember you are not draining the system you are replacing the existing water and (air) with new water via the feed valve.
  • JoeyJoey Posts: 3Member

    Great!! Thanks so much for your help!
This discussion has been closed.


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