boiler presssure

wbjeff

Recently installed burnham boiler in 3 zone baseboard house. Reused circulators and flow valves, circulators on return. Installed new #30 expansion tank, webstone exp tank service valve and webstone air separator. Week after install customer noted elevated pressure and relief valve dripping. Technician shut off autofeed and lowered pressure. In milder weather customer noted pressure would drop to "0" and top out at 18 psi when boiler running. Replaced expansion tank, customer noted pressure still rising and relief valve dripping again . Can expansion tank be undersized. thanks for your help

bburd

It’s certainly possible that the expansion tank is undersized. The size is calculated based on the total volume of water in the system.

With that said, baseboard systems with modern boilers don’t hold much water compared with older, converted gravity systems with large pipes and standing cast-iron radiators.

Was the expansion tank pre-charged with air before it was connected to the system? 12 psi is standard for a one or two story house. A three-story house needs 16 psi or so, more if the heating coil is in the attic above.

Are you sure the shutoff valve before the auto feed is 100% tight?

Is there a tankless coil? Sometimes they leak into the boiler, raising the pressure; but this would be highly unusual for a new boiler.

Big Ed_4

Where is the pressure reducing valve connect to the system ? Acts like it is connected above the circulator where there is low pressure when pump is running . Best place to connect is the PRV is the connection between the expansion tank and the system . That is the place where there is pressure change

EBEBRATT-Ed

@Big Ed_4

Thinking you meant "no pressure change"

Alan (California Radiant) Forbes

How does the expansion tank connect to the system? I've seen gunk and debris clog the connection point so that the expansion tank is ineffective.

I've also seen tank connections at Spirovents refuse to acknowledge the presence of an expansion tank, but haven't gotten to the bottom of how that happens.

wbjeff

Thanks for the reply. To answer your questions, the pressure reducing valve is tied into the system at the exp tank through the exp tank service valve. There is no tankless coil and shutoff valves are tight

Alan Welch

Is there an indirect tank?

wbjeff

There is no indirect tank

hot_rod

Alan (California Radiant) Forbes said:

How does the expansion tank connect to the system? I've seen gunk and debris clog the connection point so that the expansion tank is ineffective.

I've also seen tank connections at Spirovents refuse to acknowledge the presence of an expansion tank, but haven't gotten to the bottom of how that happens.

It's rare, but the center tube of the element in Spirovents can slide down and block the bottom connection. Usually the wire media has to be deteriorated from aggressive water.
Cody one of my Caleffi colleagues has actually seen this.
So he tells me

EdTheHeaterMan

Here is a dumb question but I will ask anyway. Was the valve between the expansion tank and the system closed?

" Technician shut off autofeed and lowered pressure. In milder weather customer noted pressure would drop to "0" and top out at 18 psi when boiler running."

I'm thinking you know better but I had to ask.

EdTheHeaterMan

The location of the circulator(s) in reference to the boiler and the expansion tank may be a factor. Can you draw a diagram?