Can't figure out why my boiler's pressure is at 30psi

Paul Pollets

There is no such thing as sizing an expansion tank "too large". However, why pay more for a larger tank than necessary? One can size a tank too small and cause the relief valve to blow. If a customer has a 145K boiler connected to radiators, I'd be using the #60 tank.

<A HREF="http://www.heatinghelp.com/getListed.cfm?id=104&Step=30">To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"</A>

Christopher_3

Can't figure out why my boiler's pressure is at 30psi

For the past month the pressure relief valve on my boiler has been dripping water whenever the boiler runs. I thought it was a defective relief valve but on closer inspection, I notice it only happens when the boiler has heated up and the gauge reads approx. 30psi. The relief valve is clearly working as designed. I've read that this can happen because of a bad expansion tank or fill valve but need a little help on this.

Maximum temp reached after boiler heats up is approx 172F and max pressure is 30psi. I've never touched the aquastat so its setting has never changed.

Expansion tank--I have one of those overhead 15 gallon steel tanks with just a gate valve on the bottom of it. The tank has no gauge or air valve or anything else to adjust. I turned off the valve going to the tank, drained the tank (far less than 15 gallons came out) and then turned the valve back on and let the water run into it ---I could hear it running for a few seconds. I know these tanks are supposed to be pressurized to 12psi---how would I do that? Doesn't the Taco pressure regulator take care of that for me or is it something I have to do manually at the tank? If there is air space in this tank, could too much (or too little) pressure in this tank be a cause for my over-pressurized system?

Pressure Regulator Fill Valve: how can I tell if this is bad? It's a Taco model 329-3 which is supposedly preset to 12psi.

I don't see a Schraeder type of valve anywhere on my system that would allow me to take a pressure reading like on a car's tire.

Could it be something else that I'm not thinking of?

Thank you for any help.

My Specifications:
-Boiler: HydroTherm model HC-145D-PV, installed 1997
-Propane fuel source, well water, single story house
-Pressure Regulator: Taco model 329-3
-Circulator Pump: Taco model 0010-F2
-Pressure Relief Valve: Conbraco model 10-407-05 (30psi)
-Aquastat: Honeywell type L8148E
-Expansion Tank: Bell & Gossett Hydro Flo 15 gallon steel "compression tank" 29.5" x 12"

Unknown

Draining the tank

Sounds like you have a "solid" or waterlogged tank. With the plain steel tank you have, you not only need to drain water, but also let air in. If you just connect a hose, open the drain valve and let the pressurized water run out, the tank will not drain completely. There must be a means for air to enter the tank. Try hanging a pail under the valve and open it completely. If air is entering you should hear a "glug" sound as air enters an then a small rush of water will follow. Continue until all water has left the tank. This should restore the air cushion and prevent the pressure from rising to the relief setting due to expansion of the heated water.

Mark Custis

Things and people wear out

Good looking out on the expansion tank. You are now, eliminating the tank, unless it has an air leak. The pressure reducing valve should allow only the set point amount of water to enter the system to gain the PSI needed to operate the system. They do gunk up.

Assuming the presure gauge is working, try turning off the PRV and draining out some PSI.

Paul Pollets

Exp Tank

I'd replace the expansion tank with a Pre-charged tank (Amtrol #30 or #60). This will greatly reduce waterlogging. All pre charged tanks lose about 1# per year and should be re-charged on yearly service. The pre-charged tanks come charged at 12PSI. Check pressure in tank before commisioning.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Thorp Thomas

Paul,

Why replace the tank with a #30 or #60 when he said it was a 15 gallon horizontal? What are the rules in sizing PX tanks and what can happen if you over size it?

Please explain.

Christopher_3

I was able to drain a lot more water out of my expansion tank. It took a while but about 12 additional gallons came out after about 30 minutes. That did the trick and the pressure relief valve is no longer dripping. Thanks for the help!

billtwocase

exspansion tank

Chris, how often is the tank filling up? possible pin hole in it. probably time to bite the bullet and put on an extrol tank

Unknown

Very easy

Just drain the compression tank , pull the drain on the tank and thread a diaphragm style right in . It won't look pretty , but it'll work

Sissy

Chris, just keep an eye on things for a while. Expansion tanks need to be drained periodically- if you find you need to drain the tank more than once or twice a year than something else may be going on. Many times systems with a "drainable" expansion tank also use the same tank for air elimination and when you simply swap a diaphragm style tank the air has no where to vent.

World Plumber

Auto vents

Chris are there any auto vent or float type air vents in the system. I have seen many instances where someone thinks they are updating the system by adding the air vents then you begin to have the relief vave drip. Air vents and the old steel tanks are a no no. You need to keep the air in the system so it can return to the tank and maintain it's compreability. You can not conpress liquid.

Mac