Boiler Purge Questions

hurleypatrick9

Hi there.

New homeowner here and novice plumber. I have a boiler with hydronic baseboard radiators. We were getting no heat upstairs (2nd floor) whatsoever, so I took it upon myself to study up and went through the purge process for that zone. Seemed to have done the trick immediately. A few questions arose however, so I want to put it to the forum for help.

1. When I went to switch the auto-fill valve to manual mode so it will flush the system with main line water and push the air out, I found a stop valve just upstream of the auto-fill valve that was closed (blue, pic 1). This surprised me, as I was under the impression that it needs to be open (at least cracked) for the auto-fill valve to do its job. However, this water supply line is split and seems to flow both into one of the circulator returns as well as the bottom of the boiler. The red stop valve was open. Which one should be open and which one should be closed? Does this explain why air got trapped in the second floor baseboards and wasn't automatically pushed through with new water? Could it have done any damage being closed? Any risk keeping them both open with the auto-fill valve on "auto" mode?

2. Some of the zones don't have stop valves (pic 2), so I had to purge the upstairs with the basement zone still open. Could that have potentially pushed air into the basement zone? Any work-arounds for this in the future so I can diligently purge one zone at a time? Could I potentially flush both at once if I can't close the zone and have access to two garden hoses?

3. When I opened the auto-fill valve and it's blue stop valve to purge upstairs, I heard fresh water flush through and watched it push air and old water out of the upstairs zone. (Good!) But, after a minute, the relief valve dumped a fair amount of water out the back of the boiler. Did I open the water main line too far? Is this expected to happen? its a 30 lb relief valve and now the pressure is about 21psi.

4. I don't seem to have any 'zone valves', or at least what I thought were zone valves. Just circulators and zone switches (electrical boxes). I do have some flow check valves (pic 3) - what do these do? Do I ever need to adjust/open/close during the purge process? Am I just not seeing the zone valves?

EBEBRATT-Ed

The red stop valve stays open. That is the cold water feed to your tankless heater. Close that valve and you will get no hot water at your sinks etc.

The blue stop valve is city cold water feeding your boiler system through the pressure reducing valve. Normally I would say leave the blue valve openbut

YOU HAVE A PROBLEM. YOUR CITY WATER IS PIPED INTO THE WRONG SIDE OF THE CIRCULATOR PUMP.

You can open the blue valve to feed the system but your automatic feeder will never work right until it's fixed Leave it closed after filling the system.

You don't have any zone valves and you don't need them your zones are done with circulator pumps

The zone you circled 'no shut off" that is a combination purge and balance valve. When you purge you use a screwdriver to close the return to the boiler of on that valve. It may be rusted up and may not work

No adjustment on the flow checks leave them as is

hurleypatrick9

Hi Ebebratt,

Hugely helpful information. It's very peculiar to me that the city water is plumbed to the wrongside of the circulator. I understand what your saying about the auto fill valve not performing as it should with the city supply (blue) closed, but if it's only auto filling *very small amounts of city water with every heating cycle (the small evaporative loss), does it really matter if I keep the blue valve open all the time? Wouldn't it just be a temporary trickle of cold city water just to top off the hydronic system? Would that trickle noticeably impact the hearing efficiency? I'm asking because I'd rather leave it open and provide continuous auto fill as needed,  rather than keep it closed and let evaporative losses confine unabated, increasing air accumulation and thus the need for purging.

Does that make sense?

You said "You can open the blue valve to feed the system but your automatic feeder will never work right until it's fixed". Why is this? Isn't it just feeding a trickle of water to keep the pressure constant and reduce air buildup?

Thanks for the education!

EdTheHeaterMan

You may find all the information you need in this booklet. I used it while teaching one day seminars on Hydronics several years ago. http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf. Understanding the system STATIC pressure and circulator HEAD pressure are key to understanding your system.

Also the reason your relief valve popped open is because you allowed the static pressure to get above 30 PSI. That happens to the best of us from time to time. You must keep an eye on the boiler pressure gauge to be sure you turn off the feed water if the gauge gets near 25 PSI. Then open the valve when it gets below 20 PSI during the force purge procedure. When completed with the purge, set the auto feed back to the automatic position, and allow the boiler pressure to go down to the required static pressure for your system. (usually around 12 PSI). Then close the purge valve to move to the next loop (or to be finished).

EdTheHeaterMan

File this under 2 ED's are better than 1

On you picture of the Flo-Check valves on 2zones and "what are these" on the other 2 zones. They are both the same thing. Taco calls them Flo-Check and Sweat-Check. Both operate identical. Also @EBEBRATT-Ed indicated the fill valve is connected to the wrong place. Here is the illustration I used to explain that issue
Consider that the expansion tank is known as the point of no pressure change in your system. (Take my word for it, because it takes too long to explain herein) so if your tank has 12 PSI air pressure in the air side of the bladder in the tank, and the auto water feed is also set for 12 PSI and you get all the air from all the radiators by purge or venting, then for all intensive purposes the 3 pressure gauges will read about 12 PSI. Without operating the burner, just turning on the pump will cause a difference in pressure between the inlet of the pump and the outlet of the pump.

Since the tank is the point of no pressure change, the gauge near the tank will stay at 12 PSI. the pump outlet will increase in pressure by less than 1/2 PSI. That is to allow for the pressure drop thru the boiler, so let's say the pressure gauge at the outlet of the pump reads 12.4 PSI. That means if the pump creates a pressure difference of about 6 PSI between the inlet and the outlet, the inlet pressure must drop to 6.4 PSI. That is just simple math. if the outlet can only get up to 12.4 PSI and the inlet is 6 PSI lower, then 12.4 - 6 = 6.4 inlet pressure.

Now look at the location of the water feeder. That is set at 12 PSI and the pipe it is connected to is now around 6.4 PSI... If that feeder is operating properly. when the pipe water pressure drops to 6.4 it will try to make it 12 PSI. Eventually that is exactly what will happen (in pretty short order too). That means the outlet of the circulator will be 18 PSI. The expansion tank will become overloaded because it will be holding 18 PSI of water and air everytime the pump operates. But after the first time the pump operates and then stops, that extra water in the expansion tank does not go away. No... Now you have about 17.? PSI as the new static pressure. Each time the pump starts up again, a small squirt of water jumps thru the auto feed valve, and eventually you will get over 20 PSI as the static pressure.

Since most relief valves are set to pop off at 30 PSI, this does not reveal itself as an issue that needs to be addressed. But if this is the way you always do it, you will come across a time when you need a higher static pressure, because you have a 4 or 5 story building. That is when you need to start at 18 PSI to get the system filled with water. If you do that when you are starting at 18 PSI and have a more powerful pump, then you will be very close to 30 PSI and will not understand "Why is the relief valve always discharging on this job?... I did it 50 times on other systems and never had a problem."

So in your situation You may be able to leave the fill valve open and let the auto feed do its job. But if you see the pressure getting too close to 25 PSI, then shut off the feed valve. You can decide to repipe the feed valve near the expansion tank at a later time (Summer Time)

(now you see why I didn't want to explain "Point of No Pressure Change" in this comment. Priv Message me if you want the PONPC discussion.)

Respectfully submitted,
Mr. Ed

EBEBRATT-Ed

@hurleypatrick9

Ok here is why it's piped wrong.

The expansion tank the air side is pressurized at the factory to 12 psi,
that's the standard fill pressure for a residential job

The PRV water feeder is also factory set to 12 psi

Those two components have to be connected in the same pressure area of the system.

Best practice is to connect them together on the suction side of the circulator (pump away) although on older jobs you will see them on the discharge side (pump toward)

What you can't do on any job new or old is what you have which is the expansion tank on the discharge and the prv on the suction side of the pump.

The reason for this is the expansion tank is "seeing" the pump discharge which is 12 psi

But the PRV is "seeing" the pump suction which is probably 5 psi

In your case the feeder set for 12 will not feed when you get low on water and

no amount of fiddeling will make it work.

If you don't care about water make up leave the feeder shut off. If you need to add water to bleed radiators etc shut the circulator off turn on the blue valve to add water and shut the blue valve when you are done. If you leave the blue valve open the way it is piped you will have issues