Going insane. H/E Pressure loss but no visible leak on mod-con...

CoHotelier

Good morning - (not sure if this should go on the wall or gas heating, mods feel free to move if necessary)

System is finned baseboard with a mod-con WM Evergreen 220 (installed 2015, existing zone piping, new primary and secondary loop to headers). Primary loop piped into boiler buddy 18gal (circa 2015). 26-99 pumps for primary loop and DHW to an indirect. Boiler had a leak at a weld on the inlet show up in 2018, the H/E was replaced in 2018. Indirect new in 2017. System has 24 zones, 2 stories, building is roughtly 20ft x 80ft.

Replaced the expansion tank a couple weeks ago, and in setting pressures turned off the Taco autofill. Taco fill set to 15psi, new expansion tank pre-set to 16psi or so.

After replacing the expansion tank, I left the autofill turned off after getting the system up to pressure. I checked the boiler room randomly on a warm day and saw the boiler system pressure was extremely low, 5psi or less. When the system turned on, I believe I heard air working through the primary. Fearing the worst, I isolated the zone side, but the pressure stayed relatively constant. I then isolated the boiler and found that over ten minutes, the pressure would drop from 18-15 or so down to about 5 or so - I don't know if I waited 15 minutes or more if pressure would flatline or not. When the boiler is isolated, that "isolation" is the heat exchanger inlet to 3ft of 1.5" piping to a ball valve that is closed at prim/sec pumps, and on the outlet side about 2ft of 1.5" piping, includes the relief valve, lwco, and pressure/temp gauge, and ends at a ball valve. (So two "dead" legs, one includes the gauge.) Relief valve is new with thermal expansion tank and is not leaking at all.

Great, so I'm assuming a leak in the heat exchanger. I take the entire H/E down, clean it, clean condensate trap, rebuild top end, new refractory, new flame sense and ignitor, etc. Before cleaning it, I felt around the bottom of the H/E with the condensate trap / lower plate/cover removed. No water. After cleaning it, while I was re-gasketing and rebuilding flue side, I dried it entirely and waited for water to show up at the bottom of the H/E. Left autofill turned on and system was at 15-18ish pressure. No water showed up, no dampness anywhere. I fully expected, at room temp, to feel or see a drip at the bottom of the H/E. I worked on it so long (probably 2 hours full dried and disassembled) that the temp dropped from the 140 or so that I started at and rested at the 100ish or so. In that amount of time (2 hours), no water ever showed up anywhere on the H/E - not by feel, drip, or visual inspection. Again, auto fill was on the whole time and held at 15-18psi.

The boiler does not pop or sizzle. My concentrate test show I still have correct levels of additive per WM instruction.

So, what gives? My concern is I have an incredibly small leak, and that I'll spend more proving there is a leak on a plumber than it's worth to just buy and replace the H/E myself. Or, that I don't have a leak and it's just some strange phenomena. Any advice is appreciated here.

tim smith

If you Isolate fill and boiler from system after cleaning regasketing, does the pressure drop like a rock still? Nothing coming out your condensate drain while isolated? Just wondering. The telltale we look for is water coming out condensate drain when not firing if isolated. As long as inside cabinet is dry.

CoHotelier

Thank you Tim - yes, inside of cabinet is dry.

What you're describing is basically what happened yesterday. I had the boiler turned off, H/E had 15-18lbs of pressure and was isolated WITH the auto fill in the loop, and over the span of 2 hours it never dripped anything out the bottom of it. The bottom of the H/E where condensate would run to and drip off stayed dry. If the autofill is off, system pressure drops about 10psi in 10 minutes, and goes to zero if I leave it for 20.

The next day I think I can retest it is on next Tuesday. It's supposed to be 55 or so outside, so I should be able to have the boiler shut down all day. I think I'm going to isolate the primary loop with autofill and the H/E from the secondary heat loop or DHW tank loop. I'm going to raise primary loop pressure to 20psi, leave the boiler off, autofill on, and leave it for the entire day and see if anything drips out of the condensate drain opening on the bottom of the H/E. I'll disconnect the condensate drain and put a cup under the outlet from bottom of H/E condensate pan.

Just trying to figure out how to surefire way to verify this and also figure out a way to effectively show it to a plumber so I don't spend a lot of money on diagnosing what's already proven to be the issue.

EBEBRATT-Ed

Strange. Is the expansion tank isolated from the hx while you are testing?. What is the relief valve setting? Maybe you can try increasing the pressure to just under the relief valve setting to find the leak.

mattmia2

Does it lose pressure if you leave everything off for a few hours to a day or so? Obviously it is going to lose pressure as the water dissolved in the fresh water you added when you refilled it and pockets of air trapped in various places work their way to the auto vent. Let it run a week or so with the auto fill on, then turn off the auto fill and see if it loses pressure.

mattmia2

Are the caps loose on the auto vents so they will vent relatively quickly (even though they may still take a while for air mixed in with the water or a large amount of air to settle out and move through the vent.)

CoHotelier

EBEBRATT-Ed said:

Strange. Is the expansion tank isolated from the hx while you are testing?. What is the relief valve setting? Maybe you can try increasing the pressure to just under the relief valve setting to find the leak.

Yes, expansion tank is isolated from the hx. Relief is a 30psi model... yes I think on Tuesday I'm going to bump the loop pressure up higher to try and find this thing.

mattmia2 said:

Does it lose pressure if you leave everything off for a few hours to a day or so? Obviously it is going to lose pressure as the water dissolved in the fresh water you added when you refilled it and pockets of air trapped in various places work their way to the auto vent. Let it run a week or so with the auto fill on, then turn off the auto fill and see if it loses pressure.

If I leave the auto fill off, that's what gets me to the position I was the day I found it at zero. What's difficult here is that even in such a small amount of JUST the HX, there's no way it's absorbing 10psi worth of air into the water. If I isolate the HX, turn off the autofill and let it slowly bleed down, when I reintroduce that isolated loop to the system, you hear the water move back to pressurize it, same if I don't bring the rest of the system into the mix and just turn the auto fill on, you can hear the water flowing to bring up pressure.

mattmia2 said:

Are the caps loose on the auto vents so they will vent relatively quickly (even though they may still take a while for air mixed in with the water or a large amount of air to settle out and move through the vent.)

I have both a honeywell vent with a cap that is loose entirely and a spirovent at the top of the boiler buddy partnered with the makeup inlet. I know that's not ideal, but the issue occurs with the vents completely isolated out of the picture.

mattmia2

So the boiler is cooling and isolated from the expansion tank?

CoHotelier

mattmia2 said:

So the boiler is cooling and isolated from the expansion tank?

I do understand what you're getting at, but in the 10 minutes that the pressure drops you'll see the temperature hasn't really changed much at all. I have pictures of the pressure gauge before and after and the temp stays the same in that time window.

Jamie Hall

You are focused very tightly on the heat exchanger. Are you absolutely 100% positive that there is no other possible leak or pressure drop anywhere else in the system? For example -- just one possibility -- there is a small leak somewhere out in the system piping. You have the valves closed off. Are the valves really closed off? There is no possibility whatsoever that one isn't leaking by just a tiny bit?

Just one example.

Step back. Take a deep breath. Consider everything as suspect until proven otherwise.

tim smith

I reread your initial description, I am thinking that you have a system leak and you got focused on the boiler. When you isolated boiler, you thought! I think maybe you have a bad ball valve still letting water go back into system where there may be a leak, if you were sure you had got most air out prior and all radiators were full. Just a theory but that's where my brain takes me.
Tim

CoHotelier

Guys, I appreciate it.  I'll take a step back and look at it again in the morning.  I am able "double isolate" the secondary loops from the boiler primary, so that's what makes me think I've got it well secured.  There are the valves physically on the primary loop as well as a pair of valves on the primary loop.  I also ordered an extra quality pressure gauge to be able to double check pressures. (I've already double checked with a rain bird hose bib.)

Unfortunately individual zones are not able to be isolated, so a system leak in the heating zones would just be a 'wait for a ceiling, floor, or wall to be ruined' approach as I already visually checked every zone and pipe run I can see.

mattmia2

Bring the pressure up to near the rating of the boiler and wait. if it goes down, note the new pressure and wait some more. if it keeps going down over a day or so it is probably leaking somewhere or one of the isolation valves isn't holding. If it stops it is probably expansion or entrained air. without the expansion tank in play, especially if most of the air is out, it takes very little loss of air or fluid or contraction to change the pressure.

The higher pressure will give it further to fall and will make it leak faster if there is a leak.

EBEBRATT-Ed

If the expansion tank is isolated from the boiler and the boiler is full of water and no air in the boiler removing literally 1 drop of water will drive the pressure down.