Boiler Pressure Relief Valve Tripping After System Repair

Nick246

Hello everyone! I'm a non-pro, first time poster here with a question regarding what could be the source of my boiler PRV tripping. So...

I have a natural gas boiler and radiators in my home, where the boiler is a Utica boiler manufactured in 1987. This boiler is located in the basement and heats only the 2nd floor (approx 20feet higher than the boiler). The Auto air vent (located on the return) was gently spewing water due to a bad seal, and the expansion tank (located on the outflow) was waterlogged. So...

We drained the system and replaced both the Tank (was initially protruding horizontally, with a little piping was changed to vertical) and the Auto Air Vent. Then tried to refill by opening inlet ball valve and.... whoops, no flow whatsoever. Determined that the pressure reducing valve was gunked up (probably 30+ years old at that point), so drained again, swapped out with a new valve, and filled the system. So far so good.

Then bled the radiators, noticing a considerable amount of air, and when they were vented completely went back downstairs and fired up the boiler. After about 45min, HAPPY NEW YEAR, the pressure relief valve trips.

Couple of further points worth mentioning:
1) this particular hydronic system has been operating for several years with the domestic inlet valve closed, and with presumably a good amount of air in the system (as i noticed when i bled them after the repair). Not sure how long its been that the expansion tank was waterlogged though.
2) the service tech who worked on the system had to replace and add a few copper elbows, and chose to braze them rather then solder them -> i dont imagine this bottlenecked the tubing from the higher heat using acetylene (it certainly looks fine) but I'm just throwing that bit out there for completeness.
3) when we fires up the system After the repair, we did so with the domestic water inlet valve ON, as opposed to the system having previously operated for quite some time with the same valve in the OFF position.

Could you gentlemen and possibly ladies share your thoughts with what might be making my boiler trip the pressure relief valve?

Gordy

What’s the psi reading with the system at ambient temperature? Should be 15 psi.

Did you have a compression tank switched to a bladder, or diaphragm style expansion tank? If so the proper psi for the tank should be 15 psi when isolated from the system.

Was the new pressure reducing fill valve set to 15 psi?

Sounds like system psi is to high causing the pressure relief valve to discharge when system gets hot.

Ironman

Can you post some pics that show the boiler, its near piping and the new components.

It could be the new tank is too small or not charged properly. Are you sure the new fill valve is adjusted correctly? Bypass fill closed?

For the life of me, I can't understand why some one would braze on a hydronic system that operates below 30 psi.

Nick246

Gordy-
Thanks for responding. As you may be able to see from one of my pictures, this boiler was shoehorned between another boiler and two hot water tanks. There is so darned little clearance that its impossible to make out the resting psi of the system without a mirror and flashlight which, unfortunately, I did not due.

In regards to the expansion tank, its set psi was not checked, but for better or worse assumed to be properly set, prior to installation. Also the prior tank was also a bladder type, with the same capacity.

The pressure reducing valve to my knowledge was set to 15psi. I screwed the top peg handtight (actually it was already by default screwed in as far as possible) which would seem to me to be its default psi.

Ironman-
Thank you for responding. I will attempt to post three pics below.

If by bypass fill you mean the inlet for the domestic water supply before the pressure reducing valve, then no - we fired up the system with that valve open. I assumed that the pressure reducing valve would take care of lowering the incoming pressure.

The fill valve is adjusted to default to my knowledge (screwing the top peg all the way downward- which is how it came out of the box).

The new expansion tank is the same capacity as the one it replaced - only its orientation was changed.


Ok some pics, from different angles:

woodrow

I am suprised the tank did not snap the piping off when it got waterlogged as far as relif valve tripping check to see what it stops at. the reason the valve was off is when the circ runs it creates lower presure and the fill valve is going to open and add another 6 psi when the water is cold depending what it set for you can have 18 or more pounds cold when it heats up it will be higher and you only have 12 psi in the tank so you loose capacity

HVACNUT

I can't be certain but it looks like the lever on the relief valve is up about 30°. Is it fully seated?
It really should've been replaced with the other water parts. They do have a life expectancy.
As with the other auto vent on the left side. Another zone return?
Hacksaw the Male adaptor in the relief discharge and install a 3/4M x7/8 compression 90° with the new relief valve.
If the boiler gauge is correct, run it to limit and keep an eye on it. It should maintain no more than 15-18 psi at limit. Between 160-180.
BTW, the PRV should be 12 psi factory. Always check, but typically doesn't need to be adjusted.

And @Woodrow is correct. All that copper out of the supply should be black iron until you clear the extrol tee, or drop theaded rod down and use clevis hangers.
Caleffi offers something to relieve the pressure on the extrol if it needs to be removed. The ball valve doesn't do anything unless someone is going to sit there depressing the schraeder. Besides, it's more fun to take them outside and smack them with an awl.

Side note for the tech. He should drop down to a #2 nozzle @ 14 psi for the compound sprayer.

STEVEusaPA

Yeah it's just piped wrong. If the expansion tank fails and gets water-logged and doesn't snap the copper, I feel sorry for the person who has to change it. You couldn't even unscrew it without getting a bath. Probably just have to drill a hole near the valve to drain it.
Could also be that copper line going to the exp tank is just clogged full of crud, and therefore is providing no path of expansion for the system to the tank. On the copper tee, where is the 'run' (going up) heading?
Keep in mind if your over shooting your temperature and steaming, you could be ruining the relief valve.

hot_rod

A few things working against you, the circulator pump is on the boiler return the expansion tank on supply, not ideal, the tank should be at the circulator inlet.

The air vent looks like it has been leaking, may not be working. It it the only air removal device?

You should add a good quality pressure gauge somewhere in the piping, the boiler dual gauges often lie

You have a ball valve near the fill valve, turn it off when the system is up to 12 psi to rule out a defective fill valve, although it looks fairly new?

Th expansion tank needs to be removed, or system pressure dropped to 0 to test the pre-charge pressure.

Add an expansion tank valve for future service.

Don't like to see tanks mounted upside down, maybe mount it elsewhere and copper or pex over to it?

Nick246

Woodrow-
Thanks. I didn't know there's a pressure drop when the circ pump kicks in (presumably only in the region by the circ pump im guessing).

Hvacnut-
The relief valve should be changed, definitely. I'm going to make sure the prv valve is set properly, though the lever was all the way down prior to it tripping initally, so assuming it wasnt defective from simply its age, when it tripped initially I'm pretty confident it was set properly.

The auto air vent in the foreground is from another independant boiler circuit, a new one put into this particularly circuit, and the pressure reducing valve is also new. Thanks for the tip about supporting the extrol, definitely a good idea.

Steve-
The copper fittings in the vicinity of the exp tank are all new, so I don't believe that theres any obstruction preventing obstruction. The run going upward from the Tee goes straight to the 2nd floor radiator circuit.

Hotrod-
Theres so much in so little of an area that optimal placement of componenets is something I'm really trying to avoid. The leaking air vent you see in the foreground is from another boiler circuit. Yes this particular circuit only has a single air vent (its new, right above the circ pump in the picture). Adding a good quality pressure gauge is a Great idea, esp since its a bear to even see the boiler's gauge given the tight pplacement of the boiler. The fill valve is new.