To get email notification when someone adds to a thread you're following, click on the star in the thread's header and it will turn yellow; click again to turn it off. To edit your profile, click on the gear.
The Wall has a powerful search engine that will go all the way back to 2002. Use "quotation marks" around multiple-word searches. RIGHT-CLICK on the results and choose Open Link In New Window so you'll be able to get back to your results. Happy searching!
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

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

JoeyJoey Member Posts: 3
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 Member Posts: 84
    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 Member Posts: 1,518

    -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 Member Posts: 3

    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 Member Posts: 84

    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 Member Posts: 3

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


It looks like you're new here. If you want to get involved, click one of these buttons!