Purging Air out of Boiler/Heating System


  #1  
Old 12-11-22, 11:29 AM
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Purging Air out of Boiler/Heating System

Yesterday I drained my boiler in order to replace the air valve and expansion tank. I thought I then purged the air out of the system but when I turned the boiler back on, I could hear water running in my baseboards, which I assume is an issue. To purge, I hooked up a hose to the drain at the bottom of the boiler with the boiler return off and made sure there were no bubbles coming out of the hose (ran for 30-45 minutes just to be safe).

I have looked up how to purge air from heating systems, but most of them have drain valves for each zone, while my system does not (house is built in 1950 and the boiler system/piping design is not optimal). I've tried manually opening a zone thermostat and draining out of the drain above the boiler (with the boiler return valve closed), but no water comes out. I even tried opening the fast fill on the pressure reducer while doing that (read it online) but it just over pressurized the system and dumped water out of the pressure relief pipe. Pressure in the system with the boiler off is 20-25 psi, so it seems normal.

Looking for any advice; please let me know if any other info is needed.


System

5 valves. 1 in attic, 3 on main floor, 1 in basement. Basement appears to have its own drain.

One drain above boiler, 1 drain below boiler. Boiler return valve is open in this picture. I cannot get any water to come out of top drain, even manually opening thermostats.

Water inlet and pressure reducer

Thin pipe is the water inlet. I'm not sure what the blue gate valve does after the expansion tank. Vertical pipe feeds boiler.


 
  #2  
Old 12-11-22, 03:20 PM
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MP,
You are going to bleed your system from that drain above the boiler on the return pipe that says 1/2" BOILER DRAIN. That is where you will bleed all your zones except your basement that has a drain above the zone valve.

You cannot bleed from the bottom of the boiler because of the way your system is fed. If you look at where the cold water is fed into the supply line it has a tee and goes into the supply and into the boiler at the same time. By bleeding through the boiler you were just draining the fresh water you just put in. The water never went to the zones because you had the shutoff closed but with the ZV's closed the water couldn't circulate anyway.

What you must do is to drain 1 zone at a time while keeping all other zones closed either by keeping stats off or even better by shutting off all blue shutoffs above zone valves and open 1 at a time.

Besides OPENING 1 BLUE VALVE YOU MUST MANUALLY OPEN YOUR ZONE VALVE WITH THE MANUAL LEVER so the water will flow through to the RED VALVE DRAIN. Finally you must CLOSE the BALL VALVE above the circulator to stop water from backing up through the boiler.

Once you get everything ready you increase the boiler pressure with the fast fill lever to 25-28psi and then open that drain valve until water runs clear. Should only take no more that 5 min. but don't be in a rush, if it still looks iffy then continue. Once you are satisfied then close the fast fill and shut the drain. Close the blue valve to that zone and continue on to the next until all are bled. You should never drop below 25 psi while doing this.

You can bleed you basement zone through the drain above the zone valve by using the same procedure.

When done bleeding, drain a little remaining water from system to about 18-20 psi and put everything back to normal and test for proper operation.

Hope this helps a little.
 
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  #3  
Old 12-11-22, 03:44 PM
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Spott, thank you so much for your help. I've tried this but cannot get any water to drain, so maybe I do not have the correct valves open or closed.

I have a hose connected to the drain above the boiler. Green valve is closed to boiler. I closed the blue gate valves above all the thermostats except for the 2nd floor zone. 2nd floor thermostat lever is set to manual open. When I open the drain valve zero water comes out. I did this earlier too after seeing a youtube video and no water came out. I tried opening the fast flow lever on the pressure reducer to see if that would push any water out, but it did not and I left it open too long so the system had too much pressure and dumped a bunch of water on my floor. Good learning experience lol!

Hose attached, green lever closed to boiler.

I've closed the gate valves above the thermostats on all zones except the 2nd floor (middle of the 5). Thermostat lever is in manual open position.

I did not touch any of the gate valves at the top of the picture from after expansion tank. Should I close those too?
 
  #4  
Old 12-11-22, 03:58 PM
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MP,
The relief valve is letting go because the water is backfeeding up through the boiler instead of going throu the zone. You have a lot of shutoffs in the ceiling fot your supply and return lines. Have you touched any, are they all open. What you can try is to bleed another zone and see what happens. You may have a bad zone valve or a bad shutoff somewhere.

One other thought. It may be early in the year but not knowing your situation, could you have a frozen pipe in that zone.
 

Last edited by spott; 12-11-22 at 05:48 PM.
  #5  
Old 12-12-22, 01:35 PM
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mopete12 system will be better with a few things.

Make depressurization and service easier installing tee with drain faucet and shut valve on line to expansion tank. Tanks are best located where easy to service/remove with ” nipple at bottom so debris does not collect on bladder shorting life

The old way to manually vent/purge at boiler was with lengthily, complex steps that did not confirm venting of air at high points of zones. After all those steps, remaining air still caused problems.

Automatic venting is easy, low cost, reliable, long term way. Best brand is Watts $12 auto vents at high points of each zone, a reliable. Many other brand vent vents, leak, have to be capped off and impossible or cannot be serviced.
https://www.supplyhouse.com/Watts-05...Vent-3679000-p

If no place to vent at high point, a quick fix is putting saddle valve on copper line to heating elements. Can be used as manual vent or connecting an auto vent: : https://www.supplyhouse.com/Wal-rich...alve-Lead-Free

A major benefit to see status and quickly trouble shoot problems, especially on multi zone systems, are pilot lights (120 or 24 volt) on zone valves, pumps, aquastat, transformers, etc..
https://www.amazon.com/dp/B0B28JBY7M...Gljaz10cnVl&th
 

Last edited by doughess; 12-12-22 at 04:35 PM.
 

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