Expansion Tank Replacement on Boiler (?)

[CanadaJasonV]

Hi All,

My first post here!

I have a Navien tankless boiler and have noticed a small leak originating from the Pressure Release Valve.

When I tap on the expansion tank it sounds fairly full.

With the exception of tasks that require a certified professional (such as gas installation), I like to perform as much maintenance on my own in order to get better understanding of how things function (metallurgical engineer by training).

I'd like to tackle this project on my own but wanted to confirm the procedure:

1. Shut off power to the boiler
2. Close the water inlet to the boiler
3. Close the water outlet from the boiler to the radiators
4. Drain the water remaining in the system -- essentially what remains in the pipes between the inflow and outflow shut-off
5. Remove the failed expansion tank (I understand it may be quite heavy)
6. Install a new expansion tank (using teflon thread tape)

And now here's where I'm unsure -- should I be:
1. Turning on the boiler
2. Opening the inflow to the boiler and then
3. Opening the outflow

Will this introduce air into the system that I need to bleed out from radiators?

Also, I believe the pressure relief valve looks okay, but I'm thinking since I'm going to all this trouble I may as well just replace it as well.

What are everyone's thoughts on all of the above?

Here's a video of my system set-up:

 

[mike fiore]

make sure you shut water feed off before draining ..looks like you have pretty good isolation valves so when you fill boiler keep valveoff on supply and return and fill slowly..i believe there is a air vent inside unit that should remove most of air while filling. then open valves and turn thermostat up and listen. if you here gurgling or water wont come back hot youll need to purge more air out.

 

[Diehard]

Assuming your expansion tank has an air fill valve(Schrader valve), have you tried releasing the water pressure and refilling the tank with 12 psi of air?
And/or confirm that the diaphragm in the tank, did in fact, fail?
I would think that just pushing in on the Schrader valve and seeing if water comes out would be verification of bladder failure.

 

[CanadaJasonV]

So I finally got around to replacing the tank last night. I shut off the boiler (power + gas) and close the water valves to and from the boiler.

When I removed the expansion tank - it was completely filled with water... And when draining it, there was a significant amount of black particulate -- as if the diaphragm disintegrated.

New tank went in with a valve to isolate it (and make any future changes easier). And the problem was solved 20min later.

Thanks to everyone for your help!