Air pocket after using tub

[Remington351]

I'll try and explain the situation as concisely as possible.

2 story home with basement in Maryland
2nd floor has two full baths. One is shower only other is tub only
1st floor has half bath
Basement has well-troll pressure tank being fed by Gould's 7gm pump at 200ft.

Problem: Whenever the 2nd floor tub is filled, I will get an air pocket in the hot water line, and only the hot water line, that gets expelled rather forcefully from the 1st floor bathroom sink hot water faucet.

So fill the 2nd floor tub, walk down stairs, open the hot faucet and after about 15-20 seconds a big air burp that interrupts water flow for about 1-2 seconds.

If I don't fill the 2nd floor tub no air pocket. Operating the 2nd floor shower does not cause any air burp.

Possibilities that I've eliminated...I think.

Air originating in well pump/line/pressure tank - I say no because no burps in any cold water lines

Check valve leaking/failing allowing siphoning back into well - no because after 7 day vacation the pressure gauge on the well troll was exactly the same.

Water heater is Whirlpool electric 50 gallon 3 years old.

Any ideas?

Thanks,
John

 

[Remington351]

Has no one ever experienced this?

 

[Sponsor]

 

[Jadnashua]

The only thing that comes to mind, and I've not connected it directly to your problem, is that filling a tub has significantly higher flow than when taking a shower.

Check the static pressure of your storage tank. To do this, turn the pump off, use enough water to bring the pressure to zero, then check the air pressure with a valve still open. It should be 1-2# below the low-pressure turn-on point of the pump controller. If you get any water out of the air valve when you check it, the tank is shot. If it is too low or too high, it can create problems.

 

[Reach4]

Check valve leaking/failing allowing siphoning back into well - no because after 7 day vacation the pressure gauge on the well troll was exactly the same.

If you have a top-side checkvalve and there is a tiny leak in the pipe, drop-pipe, or bottom checkvalve, that could cause a vacuum. That vacuum could suck air. However the fact that you only have this air in the hot would tend to argue against that. Could it be that the air gets released from the cold pipes during toilet fills, so you don't notice? Most people think that you should not have that above-ground checkvalve usually. An exception might be if you are in a state that requires such a valve. The pros and cons of an above ground checkvalve have been discussed often.

It could also be that your water has a fair amount of dissolved gases. That is pretty normal. Hot water cannot hold as much dissolved gas.

Also, is only your hot water softened?

I have not experience your symptoms.

 

[Jadnashua]

This only happens with certain chemical reaction based on your water, but the anode in the WH might be producing a gas...changing the anode might solve that if that is happening. Filling a tub might (not necessarily) use more hot water than a shower, and exhibit that problem more than other uses.

 

[Remington351]

Those are a couple of areas that I hadn't investigated yet. Thanks.