Oil burner water pressure too high.

armonkiwi

After dripping PRV that turned to more solid flow after releasing it for a moment (didn’t close off completely) and with pressure at 25psi and 165F temperature, I replaced both with new PRV and expansion tank. Both new PRV and new expansion tank were exact replacements.
Assumed failed PRV due to hard water/particles as it didn’t shut off completely at less than 30psi. However, expansion tank also full of water when removed.
Next morning water on the floor, pressure at 35+psi and temperature around 160F. PRV gushed water at slightest touch but shut off without dripping. Drained water to 20psi and shut off incoming water.
Incoming water is well water, not town supply, and goes through a pressure reducer to 12-15psi. Monitored throughout the day and ranged between 15psi at 148F and 22psi at 157F. Honeywell is set to HL of 175F.
After overnight, water again on floor, and morning pressure back to 34psi at 143F.
Boiler is only being used for heating hot water at the moment through an indirect water heater; no home heating required.
Water heater is a couple of years old and furnace and all plumbing was new in 2014.

What’s going on?! Why has the water pressure increased to over 30psi again? With the water intake still shut off, is water getting in elsewhere? The water heater piping?

Cheers

Jamie Hall

PRV -- is that pressure relief valve? I'll assume it is.

When you replaced the expansion tank, to what pressure did you set it before it was connected to the system? It must be set to the desired system cold pressure (typically around 15 psi) before it is connected.

When you say you are heating domestic hot water with the boiler, I assume that that is through an indirect hot water heater? If so, it is quite possible that there is a leak in the heat exchanger, allowing domestic water to leak into the heating system (I assume the pressure reducer is for the heating system, not the domestic). If so, try closing the valves isolating the heat exchanger from the boiler.

mattmia2

Coil in the indirect is probably leaking.

EBEBRATT-Ed

Or the new expansion tank is bad

SuperTech

I'm betting that you need a new indirect tank.  The heat exchanger coil inside the tank probably has a leak. Your water pressure is higher than the boiler pressure, typically between 30-60 PSI with a well pump. Its easy to imagine that if the coil in the indirect tank has a pinhole that it could raise the pressure in your boiler high enough to open the pressure relief valve. 

STEVEusaPA

Could simply be the water feed. Best to have someone who understands hydronics and knows how to check all the components properly before firing the 'parts' and 'components' cannons at it.

Zman

Do you have isolation valves on the domestic side of the indirect? If so, try isolating it overnight and see if the pressure still spikes.

dopey27177

Try this, after filling the system to the required water pressure and venting all the air out of the system (air is a compressible gas and when heated it will increase the pressure in the system) close the manual fill valve to the boiler and see if the water heating system pressurizes. If that happens you may have a leak in the coil that makes hot water.

Jake

armonkiwi

Thanks for all your comments! I see a thread but let me update you and see if it continues.

First of all, when I installed the new expansion tank I did not check the pressure which is meant to be 12 to 15 psi. I didn’t check because I was going away for a few days and took a gamble as I didn’t have time. So under-pressurized expansion tank might still be a cause.

However, I went away for a couple of days and shut the boiler off. Returned just now and water on the floor and the bucket under the PRV (yes, pressure relief valve) on the boiler (not the indirect water heater) was full of water. Temperature of course was down to 70F (lowest on the dial) given the boiler was off. But pressure was at 35+ psi!

Seems to me the indirect water heater has been leaking water into the boiler system the couple of days I was away. Anyone disagree? Could it still be the expansion tank? Tonight I am going to cut off the water heater from the boiler and see if it makes a difference.

One other thing. Upon return, there are rusty water stains on the Taco air scoop. And occasionally a spitting noise from its air vent. Thoughts? All appreciated!

Cheers.

Jamie Hall

At this point really the only two possibilities are the pressure reducing valve between your domestic water and the boiler fill -- if there is on (there may not be) or a leak in the indirect.

mattmia2

armonkiwi said:

One other thing. Upon return, there are rusty water stains on the Taco air scoop. And occasionally a spitting noise from its air vent. Thoughts? All appreciated!

Cheers.

Whichever thing is adding fresh water to the system, weather it is the indirect coil leaking or the pressure reducing/fill valve not holding, is adding dissolved air with the fresh water which is collecting in the air scoop. Not a cause but a symptom.

EdTheHeaterMan

Please get your acronyms right.
PRV = Pressure Reducing Valve , while
PRV = Pressure Relief Valve,
Don't confuse these two parts. You must use the correct Acronym!

Jamie Hall

EdTheHeaterMan said:

Please get your acronyms right.
PRV = Pressure Reducing Valve , while
PRV = Pressure Relief Valve,
Don't confuse these two parts. You must use the correct Acronym!

Quite. Which is why I, for one, am careful to write the whole thing out...

armonkiwi

And which acronym is which?

Jamie Hall

The other one...

JUGHNE

I have seen these labeled on prints as the "Pop Valve"