Recommended Navian NCB-240E Psi

[Marlin9393]

I did maintenance on my unit last night. I have 2 expansion tanks i changed 1 of my expansion tanks the other I took off the one I bought didn’t fit I put it back on ..The expansion tank I replace pre charged at 40.9 psi so I set my other expansion tank to 35 psi..After the maintenance I turn my Navian back on it read AIR I unplugged plugged it back in and I had hot water but now my heaters sound like water moving around the pipes is this air or did I mess something up with the PSI

 

[Plumber69]

Isnt that a combi, the boiler side expansion tank should be set at 12, not sure about domestic side, im sure that has to be higher

 

[Sponsor]

 

[Dana]

I thought the minimum operating pressure on the boiler side of the NCB series is 12 psi, and that it is regulated by an internal auto-fill / pressure reducing valve(?).

On page 8 of the manual (p9 in PDF pagination) it indicates the heating system side must be between 12-30 psi. So no WAY should the heating system's pressure be set to 35 psi or higher.

If the boiler is more than 20 feet in elevation below the highest radiator it's advisable to bump the pressure up a bit- 12psi won't work well- it's likely to collect air at the top of the system. The rule of thumb is 3 psi + elevation in feet x 0.433. There are no good reasons to run it higher pressure than that. Most (but not all) 2 story houses with a boiler room in the basement below the first floor will need to be a bit higher than 12 psi. Setting the expansion tank to the system pressure +1 psi is usually a good place to start.

You probably introduced some air into the system when swapping tanks. The air scoop & vent above the tank will eventually take care of it as long as you're getting adequate flow. It would purge the air somewhat more quickly if the air scoop wasn't so close to the 90 degree turns, which introduce turbulence, somewhat disrupting the laminar flow thorough the air scoop that lets that type scoop work. I usually shoot for a least a foot of straight pipe on the incoming side of the air scoop, but 6" will still work.

 

[Marlin9393]

I thought the minimum operating pressure on the boiler side of the NCB series is 12 psi, and that it is regulated by an internal auto-fill / pressure reducing valve(?).

On page 8 of the manual (p9 in PDF pagination) it indicates the heating system side must be between 12-30 psi. So no WAY should the heating system's pressure be set to 35 psi or higher.

If the boiler is more than 20 feet in elevation below the highest radiator it's advisable to bump the pressure up a bit- 12psi won't work well- it's likely to collect air at the top of the system. The rule of thumb is 3 psi + elevation in feet x 0.433. There are no good reasons to run it higher pressure than that. Most (but not all) 2 story houses with a boiler room in the basement below the first floor will need to be a bit higher than 12 psi. Setting the expansion tank to the system pressure +1 psi is usually a good place to start.

You probably introduced some air into the system when swapping tanks. The air scoop & vent above the tank will eventually take care of it as long as you're getting adequate flow. It would purge the air somewhat more quickly if the air scoop wasn't so close to the 90 degree turns, which introduce turbulence, somewhat disrupting the laminar flow thorough the air scoop that lets that type scoop work. I usually shoot for a least a foot of straight pipe on the incoming side of the air scoop, but 6" will still work.

I bought new expansion tank that comes pre charged at 12psi left it alone everything working fine no noise thanks

 

[Marlin9393]

Does going higher on psi give more pressure on the water?

 

[Dana]

Does going higher on psi give more pressure on the water?

If you pump air side the expansion tank to more than 1-2 psi greater than the system's idling pressure it ceases to behave as an expansion tank until/unless the water's expansion reaches the same pressure as the tank. Pumping the tank to greater than the system pressure pushes the bladder in the tank tight to the water connection inside the tank, and it no longer behaves as a shock & vibration dampener. Pumping in more air will only increase the water pressure on the system until the tank is completely full of air (having pushed all of the water from, the expansion tank back into the system.)

The tank may have come pre-charged to 12 psi, but what does the system pressure read when no pumps are running?

 

[Tankless]

If you pump air side the expansion tank to more than 1-2 psi greater than the system's idling pressure it ceases to behave as an expansion tank until/unless the water's expansion reaches the same pressure as the tank. Pumping the tank to greater than the system pressure pushes the bladder in the tank tight to the water connection inside the tank, and it no longer behaves as a shock & vibration dampener. Pumping in more air will only increase the water pressure on the system until the tank is completely full of air (having pushed all of the water from, the expansion tank back into the system.)

The tank may have come pre-charged to 12 psi, but what does the system pressure read when no pumps are running?

Hey Dana... just reading the last line of your thread and need some advice. I have a Navien NCB 210-E combi boiler that I just installed. The unit is set for 12psi and my expansion tank is also set at 12psi. The only way I can run it without the make-up water coming on is by setting the system, when idle, to 17.1 psi and closing the make-up water valve. When the heating system is running, the psi on the unit displays around ~24psi. I don't have a pressure gauge on the supply side of my system (only the one on the unit display), but I do have one on the return side and it reads a constant 15psi all the time, running or not. The heating system is working well as long as I keep the make-up water valve closed and don't mess with it. My question is why does the make-up water go above 12psi when that's what it's set for on the unit? The system is tight and there is no pressure loss. Also, if my system is running between 15-24 psi, should I add some air to the expansion tank? I'm not a plumber or a contractor, and before this project I had never even soldered pipe. I'm pretty damn proud how I designed and built this system, but I still need to figure out how the pressure thing works. Thanks.

 

[Jadnashua]

When the ET is sized properly for your system, the pressure will still rise a little as the water is heated. How much depends on the rise in temperature and the amount of water in the system. Oversizing the ET doesn't hurt and that minimizes the pressure rise on both the boiler and on the potable water side, too.

If the water pressure continued to rise, that could indicate either an autofill fault, or a leak between the boiler loop and the potable water, potentially in the heat exchanger.