I've got an old ass boiler with a 30# Extrol expansion tank that is overpressuring (~32psi) when under load, and allowing water to leak past the pressure relief valve (as it should).
I shut off the water intake valves and killed the power to it overnight, and released pressure enough to stop it leaking past the relief valve. This morning I was at ~10psi @100°F. Firing it up, it heated the water to ~175°F @ 18psi and held with no leaks. When I turn the thermostat on so that the water circulates to the baseboards, temp dips (obviously) and as it heats, climbs to ~32psi where it starts leaking past the prv again.
This is the first time I've dealt with a boiler, but pretty much everything points to the expansion tank being the issue. The diaphragm appears to be intact (tap test checks out, and I can feel that warm water is only entering the portion it should be). At this point, I suspect that the issue is low air pressure in the expansion tank, however, in order to test or recharge it, I need to remove it from the system.
Everything online states that I should simply turn off the isolation valve for the tank and remove it, but whoever put this bad boy together decided an isolation valve simply wasn't needed. This means I need to drain the whole boiler in order to pull the tank.
Does anyone have advice on how to do this? I am on single zone heat circulated by the taco pump and hot water for faucets is distributed via the mixing valve. In order to drain it, I believe I need to turn off the valves for water intake as well close off the valves for the heating system post-taco pump and post-mixing valve for the hot water line. Then I can drain via the lowest valve on the front under the oil pump.
However, how do I ensure that no air remains in the system when I'm done? Do I need to bleed at all the hydronic baseboards as I refill the system? Is there something else it could be besides low air pressure in the expansion tank? Am I just moronic?
Close up picture of the expansion tank. I believe that's an air bleeder at the top of the connecting T but am not 100% sure about that. I just started learning about these last night. If so, is that a sufficient means of ensuring no air remains in the drained portion of the boiler before I reopen the valves to allow full circulation with the rest of the system?
im pretty sure your coil for domestic hot water is leaking.
Would I not see water accumulation elsewhere if that were the case? The only time I see water exit the system is via the pressure relief (T&P) valve when system pressure exceeds 30psi. As soon as the pressure lowers below 30, no water exits the system.
the coil itself could be have a pin hole. This can feed the boiler more water than it needs on the heating side, there by increasing boiler pressure and popping the relief once it hits 30psi. if the expansion tank is good, and fill valve is good, then I'd point to coil. That's the only other place I can think of where water will be able to get into the heating side and increase pressure.
Thanks, anon! That helps a lot. Any specific troubleshooting steps you'd recommend for testing to see if it's the coil or is that more of a "drain it and pull the thing to inspect" kind of deal?
Also, correct me if I'm wrong but the coil is contained in the large circular piece stamped In/Out where the pressure gauge is mounted. There is definitely signs of corrosion, but that was from a previous issue that the previous homeowners repaired. There is no indication of water leaking from that area with my current issue.
It's hard to make out the exact layout from your pic, but the valve might not be right next to the tank. I see a yellow ball valve to the left and what looks like another valve past the motor.
Here's a better picture of the line running to the expansion tank. I'll follow up with some More pictures showing the rest of the layout and valve positions.
Here's a pic of the yellow and red isolation valves post taco pump.
From that picture it looks like the ball valve before the fill valve is close. what you can do is leave it close and mark the standing pressure. of course it'll raise when applying heat, but it rising to 30, and that valve being closed ,makes me even more certain now that the domestic coil has sprung a leak.
keep that 1/2 ball valve before the fill valve close and observe the pressure. see how high it goes when firing, really shouldn't go more than 20-25. If it does, it can't really go past thirty because the relief valve is working, but I'm sure about my theory right now.
So I haven't tried firing it up with the valves closed before the fill valve to observe pressure, but I did close them off and kill power just to be sure nothing was leaking out while I wasn't babysitting it. I'll try firing it up with the valves closed and watch the pressure.
Pressure dips as the temp drops, but with a coil leak would I expect to see a slow, consistent decrease in pressure in the current state with the fill valve isolated from the system once the water is cooled to ambient room temp because of water leaking from the closed system and not being able to be replaced via the fill valve?
you'd observe an increase in pressure. the domestic water is forcing its way into the boiler. raising the boiler pressure.
I think I might be misunderstanding how this portion of the boiler functions. If I have the fill valve shut off, how does the domestic water supply feed into the boiler? Thanks a ton for all the answers, anon, this is super helpful to a noob like me.
domestic water and boiler water aren't supposed to mix. the side marked " in " on the coil feeds into the coil from a "separate" cold water line. to put it simply the domestic side has its own feed independent of the line supplying water to the heating side of the boiler.
Gotcha, I just went down and took a look at the lines again and that makes perfect sense now. I tested with the fill valve isolated and it overpressures still so I think you're correct that the coil is leaking somewhere. Merry Christmas, anon, truly appreciate all your help!
Alright, I've got it all fixed up. Turns out it was just low pressure in the expansion tank. Draining was easy, but even though I isolated the baseboards I got a frick ton of air in them because it turns out my bleeder valve on the T by the expansion tank was bad as well. It let out some air so I thought I was good, but when I filled and turned it all on it started chugging like a motherfricker. Ended up bleeding at the baseboards, but still could tell air was trapped in the system. I drained again, replaced the bleeder on the T with a brand new one, refilled and got a ton of air escaping this time. Reopened the baseboard lines and bled at the baseboards while I did the dance of the drain and fill. Took me 3 hours of running up and down the stairs but now all the baseboards are warm and I've got stable pressure.
I did all of that with the domestic water loop isolated, so once I was sure the low tank pressure symptoms were alleviated and everything was working as expected, I reintroduced the domestic water and saw no change in pressure (imagine my relief).
Bleeding everything turned out to be just as big of a pain in the ass as I thought, but probably would have been easier if my main bleeder were functioning properly to begin with.
I'm going to make the old bleeder into a christmas ornament so that my family will always remember Chillmas.
I understand how to bleed and why it's necessary, I just needed to know if bleeding the baseboards (essentially radiators in this case) was necessary if I isolated them from the boiler while draining it. I believe the answer is that it is not necessary when they are properly isolated IF you have a working bleeder on the boiler, which I did not. Once I put the new bleeder on the boiler the amount of air escaping was significantly more noticeable, but I had already introduced air into the baseboards unwittingly so I got to bleed everything.
Ah, that helps a lot. Consider using dry ice.
And yes you need to bleed. You can also get automatic bleeder valves.
Thanks! I'm assuming I have a manual bleeder valve at the top of the T off the expansion tank. If the boiler is isolated from everything post-taco pump when I drain, can the system be bled entirely from this bleeder valve or do I need to bleed from the baseboards afterwards as well? Do the taco pumps have air bleeders built in that I could purge from before opening the valves back up?
Bleeding has to be done at every high spot. I'm not sure about baseboards but big radiators need to be bled because water flowing is not enough to displace the air. Look it up online, you'll find lots of explanations. This Old House as a segment on bleeding radiators and they explain the reason nicely.