Pressure rises, does not cool when boiler cools

dyi13 · July 2015

I have a 131,000 boiler that heats the baseboards in 4 zones plus an indirect water heater. Since it's summer, only the water heater has been using it. It has always been a cold start system, only fires when a zone is requesting heat. I noticed the pressure relief valve dripping, so I drained the old steel expansion tank and restarted the system. The pressure rose from 14 to 17 when the boiler got to 180 degrees, and when it cooled it stayed at 17 psi--did not return to 14. It got to 25 after a few days. After draining the expansion tank a few more times to no avail, I replaced it with a bladder type, 4.4 gallons. Drained some water to get the pressure back to 14 when it was 110 degrees. Starts it, goes to 17 when it gets hot, and stays there when cools down! Today I opened all the zones and started the heat. All rooms got hot, but pressure got up to 20 psi. Is down to 19 psi now, we'll see how low it goes when the system cools. It's not the automatic fill, as I've had the valve that feeds it shut off for a few days, and pressure still rises. The automatic fill must be set to 14. I cannot believe its the indirect hot water heater, as it is only 2 years old, and pressure does not rise unless system is firing. I do notice that with the new expansion tank, the pipe that leads to it does not get hot until around 130 degrees, 17 psi. The expansion tank uses the same input pipe as the old steel tank. Hot water is on top, cool on the bottom. Any ideas? Thanks for any insight.

Steamhead · July 2015

Shut off the water to the indirect and see if the problem goes away. If so, there's a leak in the indirect.

What brand is the indirect?

dyi13 · July 2015

My indirect is a Weil McLain Aqua Plus 45. Boiler is also a Weil McLain 131 btu, 18 years old. So when the boiler cools to 130 or so, I will isolate the indirect (there are shut off valves boiler supply to water tank and return from tank), close the boiler fill valve, drain the boiler to 14 psi (that's what the auto fill is set to for some reason--do I need to open the zone valves prior to that draining?), open a room zone to call for heat, and see what happens--is this correct? Thank you so much for your reply.

Additional info: Last night the pressure did go back down to 17 after the boiler cooled to 115 this morning. But for some reason, it is stuck at 17, even though I initially filled the system 2 days ago to 14.

billtwocase · July 2015

I would also set the pressure to 12-14, and shut of the feed valve. could be no good. Pics always help

dyi13 · July 2015

Do I need to open all the zone valves before draining? Pictures are hopefully attached. The feed valve is off. Thanks for your help.

4Johnpipe · July 2015

Check the pressure with a gauge of the EXP tank when cold. Remove it from the drop ell and check it disconnected from the boiler.

dyi13 · July 2015

An update: This morning when the boiler was at 100 degrees, I opened all zone valves and drained it to 12-13 psi (maybe 1 quart of water to lose 4 psi), closed the water fill valve, isolated the indirect by closing their valves to the boiler, opened the zones, requested heat via the thermostat for one zone and fired it up. By the time the boiler temperature got to 120, it was at 16 psi and the warm water started traveling up the pipe to the expansion tank. It got as high as 18 psi at 180 degrees and I've been watching it cool (it's off). It's now at 120 degrees and 16 psi. As the fill valve and indirect valves are closed, no new water can possibly get into the system. Is the extra 4 psi air?? Is that why I am gaining psi even when cool? Is it proper behavior that water doesn't start flowing to the expansion tank until 16 psi? I have not yet checked the expansion tank--it's brand new, and since water doesn't start going there until 120/130 degrees and 16 psi, I don't understand how it could be the tank. Can someone enlighten me? Thank you so much for all of your help.

billtwocase · July 2015

First, you don't need to open the zones to take the pressure off the system. I would like to see better pics of the extrol piping, and feed valve piping. I cant see how it is hanging. I would also purge the system, as it probably has air in it now.

dyi13 · July 2015

Here are, I hope, better pictures of the expansion tank and feed valve piping. I did fire the boiler back up after my experiment, and psi goes no higher than 18 even though it now started at 16. The main fill valve is still closed, and for the experiment, I did isolate the hot water tank. I would really like to understand this. Thank you!

Two additional perhaps unrelated notes: pressure relief valve is still dripping, maybe 1/8 cup per day. I don't believe it reseated properly. Also, the one circulator pump goes on when room zones call for heat, but
not when the indirect calls.

billtwocase · July 2015

When you replace the relief valve, and you will need to, all the drop should be copper and not iron. That is a no no. Second, still cant tell, but is your indirect on a zone valve or an additional circulator? If you haven't lost hot water, it has to be pumping the hot water thru the coil somehow

dyi13 · July 2015

The indirect is only on a zone valve. Perhaps because it is so close to the boiler, gravity takes care of it? I can feel that the pipes going to and from the heater are very hot when the system is firing.
F
That pressure relief valve was replaced two years ago. Any chance on reseating it? If I do need to replace it, do I need to drain the entire system since only two of the 5 zones have shut off valves?

Also, did I hook up the expansion tank correctly? It is 1/2 inches pipe just after the first air vent valve; that's what was there with the old tank.Any idea why the system refuses to return to12 to 13 PS I? Thank you so so much!

Paul48 · August 2015

My theory.........You are pumping at the point of no pressure change, and that is the source of your pressure issue.

dyi13 · August 2015

Sorry, Paul48- can you explain? My system is at a stable 16 cold-18 hot right now. No new water is entering the system. Only the indirect is calling. I guess the big question is, is this ok? Thanks, I appreciate everyone's comments.

billtwocase · August 2015

Just a couple of LBS gain is OK.

dyi13 · August 2015

Thank you, billtwocase, I can rest a bit easier. It is a mystery why my boiler won't go back down to 12-14 psi when cool, though!

Paul48 · August 2015

My theory is wrong...I forgot you shut the supply off.

dyi13 · September 2016

An update--it turns out, it was a defective Weil-McLain Aqua Plus all along. Pressure was stable at around 16-17 (still too high) for around 8 months, and then started rising again. Turns out the water heater coil was leaking. Probably was defective from the beginning!

At first Weil-Mclain did not want to honor the warranty because I did not have the annual maintenance done. The plumber had to take a photo of the sacrificial anode (which showed some corrosion), and that caused warranty problems. While Weil-Mclain finally did give me a new tank, they refused to pay for labor. Counting the double labor, that tank cost me nearly $3,000!

Based on my experience, I would not recommend Weil-Mclain. The old tank lasted 17 years without maintenance! They obviously don't make them like they used to.

Pressure sitting nicely at 13 now

. Thank you all for your help, DON'T INSTALL WEIL-MCLAIN!

Pressure rises, does not cool when boiler cools

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