Condensing boiler high pressure

[JFCarbonneau]

I have a 5 year old Viessmann Vitodens 100 and in the past few weeks, it started losing water from the relief valve. When the boiler is not in use, it indicates a pressure of ~12 PSI but when it is on, pressure increases to 32ish. I changed the pressure tank but the problem remains. Any suggestion?


Thanks


JFC

 

[Reach4]

I don't know boilers, but I have seen some posts.

Did you set the air precharge to 12 psi or buy one with the precharge already at 12 psi? If you bought one for water heaters, those come precharged to a higher pressure.

 

[Sponsor]

 

[JFCarbonneau]

I don't know boilers, but I have seen some posts.

Did you set the air precharge to 12 psi or buy one with the precharge already at 12 psi? If you bought one for water heaters, those come precharged to a higher pressure.

it is a WATTS ETX-30 pre charged at 12 psi.

 

[NY_Rob]

Try running it with the make-up water auto feed valve shut off... it can't add water if the valve is shut off.
If it still increases pressure at that point, either the new exp. tank isn't pressurized correctly or you have a blockage leading to the exp. tank.

 

[Dana]

If the auto-feed were seeping the system wouldn't return to 12 psi when cool- it would keep creeping up.

Check the pre-charge on the expansion tank, and make sure it isn't being isolated from the system with a valve. Just because the factory pre-charges it to 12psi doesn't mean it always stays there, and it always needs to be verified and adjusted (harder to screw up if tested before it's installed) prior to pressurizing the system.

An under-sized expansion tank can also have that symptom, but it doesn't change over time. If the new tank is the same size as (or larger than) the one it replaced, and the system hadn't experienced high pressure previously it shouldn't be happening now unless improperly charge (or failed, dead on arrival.)

Just for yuks, check the pressure on the tank with a tire pressure gauge the next time the system is gauge is reading 25-30 psi. If the tank is still 12psi (and not 25-30psi) , it's isolated from the system.

 

[JFCarbonneau]

Try running it with the make-up water auto feed valve shut off... it can't add water if the valve is shut off.
If it still increases pressure at that point, either the new exp. tank isn't pressurized correctly or you have a blockage leading to the exp. tank.

Thank you NY_Rob, I changed the auto feed valve and everything works fine now.

 

[NY_Rob]

Thanks for posting back the results!