Baseboard hot water heat - gurgling noise in piping

[goshenHeat]

I am hoping someone can explain the following situation.

My home has baseboard hot water heating using an oil fired furnace. The water piping is a closed loop system. There is an inlet valve for make-up water, but the valve is closed. There is an expansion tank on the outlet water pipe from the furnace, and the air pressure in the tank is at 12 psi (I checked). There is an air purge on the outlet water pipe from the furnace, and it does work because I do on occasion hear air escaping from the purge valve.

Occasionally I hear gurgling in the water piping in the house. I assume that the gurgling noise is due to air pockets in the water. The furnace is 4 years old and I have seen no water leaks that might allow air to enter the system. I never have to add make-up water to maintain the water pressure. I have seen no water leaks from the system. I assume that if water was leaking, the water pressure would decrease over time.

What is interesting is that the gurgling is noise is heard only every few days. Strange!!

If I have an air purge, I would think that the air would eventually be purged and I would no longer hear the gurgling. And since the water piping is a closed loop system, no air can enter the piping. I would think that eventually all of the air would be purged and I would no longer hear the gurgling. So why does the gurgling continue year after year? What am I not understanding?

[HayZee518]

water when heated will dissolve out oxygen and hydrogen out of liquid over time. it is this mixture that you hear gurgling through the pipes. the gas seeks to find the highest level in the system and it's HERE that it should be vented.

[Redwood]

Some systems do not have bleeders at the high point.
On these a hose is placed on a drain by the boiler, with the circulator off, certain valves closed, and fill water is run through the system to force the air out the hose because of the high flow rate. It is probably best if you could have someone that knows what they are doing show you how to do it if you don't have bleeders.

[jdc0222]

I think the inlet valve should be kept open. That will replace any water that vaporizes and escapes through the purge valve.

[Redwood]

Originally Posted by jdc0222

I think the inlet valve should be kept open. That will replace any water that vaporizes and escapes through the purge valve.

That would be correct!
Good catch!