Boiler relief popping intermittently over the years

fieldmatt2

Hi Guys, i know this is probbaly the 1000th forum out there on releif valves, and im a fairly seasoned tech and have worked on dozens, maybe hundreds of boilers before, however i have a bit of a head scratcher, and just wanna see if i can get some outside input. This is goning to be a bit of a read, but i would appreciate if anyone has some constructive input.

We have a customer who is an older woman, and has been using us after her last company couldnt seem to help her out. Someone replaced her boiler with a utica/dunkirk cast iron boiler, but didnt change out any of the surrounding piping, zone valves, wiring, or anything else, job looks like a total mess. According to date on the unit it was installed in 2010, and she moved in around 2015, and did not have any problems with it. One day in 2019 she had a pipe blow in her upstairs bathroom, and hired a gentleman working with her insurance co. to fix all the damage. Apparently he hired some hack job plumber to fix the plumbing upstairs, and she said he was doing something with the boiler, changed a bunch of parts, (she doesnt know what parts or why he did that exactly) and he didnt give her a receipt. Ever since then shes been having intermittent issues with the releif valve popping off, sometimes it will pop of consistently for a couple of days in a row, and then it will stop, be fine for a month, and start again. She called an hvac conpany who was unsuccesful in trying to figure out the problem, and we are the second company out there. Ive been back a few times just trying a few different things just to see under what conditions the releif will and will not go off.

First thing i did when i came out was a i drained and changed the releif valve with a fresh 30psi releif valve, it was pretty crusty looking, and i replaced the p/t guage, the old guage said i had 15 psi after i drained, so i changed it out that way i know i have an accurate guage. I filled to 12 psi, bleed, and told her id be back in the morning to check, and put a bucket under the drip tube for the releif valve. I come back the next day and the bucket is halfway full and prssure guage is just under 30, water trickling out slowly into the bucket. I drained it down again, prssure in the Expansion tabk was a little low at 12, however i changed for a fresh tank, double checked air pressure was at 15, and was also considering that the fill valve might be over filling, so instead of changing it, i filled up and bled the boiler, pressure was sitting right under 15, and i shut the incoming water off. Ran through a full cycle, got up to temp, shut off, pressure held steady. I told her i suspected that the fill valve might be over filling the boiler, and she asked if i could change it just to be safe. So i changed the fill valve with a watts 1156, set for 12 psi. I let restarted the boiler, and seemed to be ok but noticed pressure was slowly creeping up, but not much. I told her i would come back at the end of my day and double check. I leave and return about 5 pm, pressure is up to 30psi and releif is leaking into the bucket again. At this point she starts telling me more about the original plumber who was here in 2019, and thats when all this started happening. I started to more closely examine what he might have changed about the boiler, nothing too obvious stood out to me, but i did notice a few things. 

-Expansion tank is located on the supply before the zone valves, and it appears the pump was replaced with a taco 007-F5-Ifc, which i dont beleive and IFC flow check pump would be the original pump on a utica boiler.

-The fill valve is piped into the return, just above, (on the suction side) of the circulator pump

-All 3 Zones are piped in 3/4 copper, however the return for all 3 zones tie into (1) 3/4 copper pipe, which goes to the suction of the circulator/inlet of the circulator pump. Im thinking this may cuase a pressure drop where the fill valve is piped in, and would explain why we didnt have this issue when i turned the imcoming water off.

-The fill valve is on the return, and expansion tank is on the supply. Typically i would pipe the fill into a tee with the expansion tank. 

-The expansion tank, is before the zone valves, which are taco 570s. Being a directional zone valve, i think they would act as check valves, and the ifc on the pump is also a check valve, the exp tank is effectivly checked on both sides, and may see different pressure than the fill valve?

Between my urge to figure out problems like this, and my soft spot for sweet old ladies, i really would like to figure this one out for her. We agreed not to take anymore money from her besides the initial service call until we 100% figure out whats going on here. I also dont like being a parts changer and dont want to keep changing parts at random until i know whats going on. Ill try to attach a few photos of her boiler setup. I told her that the way to solve this may be that we have to do some repiping. She didnt have a problem with that, however is concerned that either it may not fix the issue, and that it was always piped that way, for years before she had this problem with it.

fieldmatt2

Big Ed_4

The problem is they piped the boiler feed above the circulator , The best place to pipe in the pressure reducing valve is the connection between the expansion tank and the system . We call it the point of no pressure change .

The circulator kicks in and now the lowest pressure in the in the system is upstream of the circulator , the pressure reducing does its thing , valve opens up adding more water to the system...

To get out back off on the feed...or repipe

EBEBRATT-Ed

Can't see the circulator but the expansion tank and the water make up have to be on the same side of the circulator not one on the suction and one on the discharge which is what you may have. I would also take the expansion tank off the boiler and check the air charge. The expansion tank and water prv should be set to the same pressure 12-15 psi.

fieldmatt2

I know i shouldve taken a better picture that shows the whole thing. The circulator is a 007-f5-ifc, and is right below where you can see the prv tie into the return. Pump is installed to pump downward into the boiler. I agree that fill valve and exp tank should be piped together, and on the same side of the circulator. 

This is what i was trying to tell her, the boiler wasnt piped right from the get go

Question is, with the fill valve on the return/ suction side of the circulator, does the expanion tank count as being on the discharge side of the circulator, or is that on the suction side of the circulator?

hot_rod

The expansion tank, where ever it is piped in a system established the point of no pressure change
The fill valve needs to tee in there

Ideally the circ should be right after the tank. But systems can work with the pump in the return

I think @Big Ed_4 has it correct, the fill sees the pressure at the suction side of the pump,’which drops below static fill

But  turning iff the fill valve should  eliminate that  option. Assuming the fill valve is off tightly

pedmec

your expansion tank is on the discharge side of the circulator. you can drop the expansion tank and install a tee between the air scoop and the expansion tank. tie your water feed into the branch of the tee. now your water feeder should be unaffected by the circulator (point of no pressure change). i like to put a tee handle ball valve under the air scoop first so i can isolate the expansion tank and water feeder so i don't have to drain the system to replace those items.

is this all baseboard heat or is it radiators>

fieldmatt2

@pedmec yes its all baseboard, no cast iron radiators. @hot_rod and @Big Ed_4 i agree the fill valve should be piped with the tank, thats how we usually do it when we install new boilers.  Just for the sake of conversation, can we clarify the point of no pressure change? I understand the concept, but what specifically is the pressure not changing from? Not changing from pressure due to expansion when the water heats? Its been along time since going over this in school

SuperTech

The points of no pressure change is where the expansion tank, air eliminator and fill valve should be. If you have 15 PSI with the circulator off, when it comes on you have more pressure on the outlet of the circulator and less pressure at the inlet. The expansion tank is the only point in the system that the pressure doesn't change when the circulator runs. The founder of this website wrote an awesome book on this that I highly recommend, "Pumping Away" by Dan Holohan. 

The fill valve is in a bad location, but the first thing I would do is isolate and drain the pressure off the expansion tank and check the precharge on it. I wouldn't be surprised if it was low on air pressure or had no air pressure in it.

hot_rod

You create the point of pressure change in a system. You do this by choosing where to install the tank.

The tank could be on the roof of a tall building and the boiler in the basement for that matter. The tank up high with the pump located there could cut down the size of the expansion tank considerably on a big volume job.

Them key is understanding how and why PONPC has such an effect on a system. Especially a problematic air system.

Sometimes a graphic like this helps "see" how the tank and circulator interface. In this example the circulator is able to add 9 psi of pressure to the static fill pressure. Call that delta P, or dynamic pressure, pressure added when the circ spins.

As flow goes around the circuit that energy, delta P gets used up so to speak, overcoming the flow resistance in the piping, radiator fittings, valves, etc..

fieldmatt2

@hot_rod, the graphic makes total sense, i appreciate it. Reminds me of the stuff we were taught in school. We did a repipe of the customers boiler and reloacted the prv to tee in with the tank, as well as replacing some older valves and piping that was starting to drip. Everything seems to be working fine now. I appreciate everyones input!

hot_rod

Here is where it starts to go south. Low fill pressure from inaccurate gauge, 5 psi in this example, reading can allow for negative pressure conditions.
Or a high head circ developing 12 or more delta P, even with a 12 psi static fill pressure.

An auto air vent anywhere along the piping at 0 or lower pressure could allow air into the system.