STEAM, Indirect loop getting air bound all of a sudden

Unknown

Hello,



I have a unique issue that I am hoping someone can help me with. I will try to get right to it as quick as I can.

~5-6 year old burnham steam 4 section boiler. I replaced this back then and re-connected to existing indirect piping in same location (was the same boiler) thus no configuration changes at all. Everything worked well for years.



Fast fwd....2 months ago we replaced the block under warranty from burnham, leaking (big surprise there). Same block, plug and play, removed and re-installed again just using couplings in the indirect loop, same exact configuration. Well...since the new block or shortly thereafter it has been getting air bound on the indirect loop. Makes no sense to me as there are literary no changes to the piping configuration.



So, although it was working for 10+ years as it was, no we are getting air bound and it is my fault. Despite that it was not piped how I would have piped it....it was working fine.



So today I bit the bullet and re-piped the entire indirect loop (40 gallon superstor htp) using Dan Holohan's piping diagram to the "t". The supply comes off of the right side (looking at it) of the burnham on a 1 1/4 block tapping. This is about 2-3" above the 3/4 draw off tapping in the back on the same side. From that supply tapping I have the following in order: Shut off, purge, Tee (bypass coming in tee), pump pumping away from boiler to tank, temp gauge, check valve (sweat), then into tank. On the return side...back left of boiler it goes into a tee on the cast iron/black at the bottom of the boiler. From the boiler on the return I have, ballvalve, purge, tee (bypass 3/4) sweat check, then to tank on bottom tapping (return). All piping is 1" copper, bypass is 3/4.

I filled the system via a hose as Dan states to, and thought I was good to go. The temp on the supply is set to 180F while making steam via the bypass.



After several start stop cycles, the son of a gun got air bound again, despite a very through initial purge that I know did not leave any air in it. SO....after a lot of testing....what is happening is this.....if I activate the DHW pump via the aquastat on the tank, it starts and for the first 4-7seconds it gargles and makes noise as if it is pulling in air. Then clears up. It does this sometimes while others it does not and starts up mint with no noise. I tested it a lot, and it only got air bound once so that I had to open the return purge and I got about....10-15 sec of air before water out of it. I know I will get a call back in a day or so with it air bound again.



I really do not understand why this is happening all of a sudden, and especially with the piping done 100%, triple checked to Dan's specs.



Any ideas much appreciated. The only thing I came up with, is that when she is tea kettling, air is getting in the supply and causing this issue. BUT...there's no way to prevent this right....it is inherent in how they work. Would moving the supply down to the bottom of the block (I could use the draw off location) help reduce this as there will be less air down there? I do not think it would make a difference in reality.



Also I should not that although I got a ton of air out, I am not sure whether or not the pump would have pushed it through if I let it, but my gut tells me no, it would not have and I would (will be!) getting the call.



Simple block replacement and now I am stuck re-piping the entire indirect loop.



All thoughts welcomed and appreciated, thanks all!

Unknown

update

I did just read on another site that the supply piping should 90 down right as it comes out of the boiler. I did not see this in any other diagram, just this one site. I did not do so, I came out horizontally with the aforementioned fittings and did not 90 down to the indirect until after the check valve. I can't see this really making a difference...and none of the other diagrams I have seen state this. It would be a major pain and re-pipe to change it now!

Mark Eatherton

Fairly simple idea...

The supply and return MUST come off below the minimum standing water level of the steam boiler, preferrably as low as possible. The circuit MUST be completely purged of any and ALL air. There can NOT be any type of automatic air elimination device (think auto vent) within that circuit.



If you have a check valve in the circuit to stop gravity thermo siphon, then you will NOT need the thermal siphon trap you found on another site.



Purging is a function of getting adequate velocity to push the air out of the piping like a piston. In as well as out. THe fact that the pump sounds air bound when it first starts almost indicates to me that you have not gotten a complete purge.



There is also a possibility that the seal assembly (assuming the use of a 3 piece circulator) could leak air in under a negative pressure, but not let water out when under static pressure, causing the loop to become air bound.



Got pictures?



ME

Steve Whitbeck

Low pressure point

Is the pump on the supply side? If it is it could cause a lower pressure point inside the pump and it could flash to steam if the boiler is running in steam heating mode. I install a aquastat below the water line that shuts the burner off in indirect mode at 180* if the space heating thermostat is not calling for heat. ( it will then use the pressuretrol for burner control)

What type pump did you use  ( wet rotor - bad choice ) did you install a Y strainer in front of the pump.

The wet rotor pumps are high RPM and have very small openings in the impellar. You may have debris in the impellar.