New Boiler Pressure Relief Discharge Post-Mixing Valve Install

digger5150

Something happened to my original post - I'm trying to recreate it now…

About 3 months ago, we had the domestic water mixing valve swapped out by a plumber in an effort to obtain more consistent hot water in our 2nd floor shower. This was after I had already changed the local Kohler mixing valve in the shower to little or no affect.

The new valve did make a big difference and I consider that issue solved.

About 6-8 weeks ago, I started noticing water in the left-side mason jar on the floor under the relief valve pipe. This is the first time I've seen water in it in the 5 years I owned the house. When I bought the house in 2021, the mason jars were there, but up until this time, they were bone dry.

Now I'm seeing water in the left-side jar that will fill it roughly every 10-14 days. I don't think it started immediately after the mixing valve swap because I would have connected the two and immediately called the plumber back to look at it. It's definitely some time after that.

I put these facts and pictures through AI which said it is caused by 1) sediment stuck in the automatic relief valve, or 2) A failing expansion tank, or 3) an internal tankless coil leak.

However, I don't trust AI so that's why I'm posting here.

Is this pressure relief issue related to the mixing valve swap, coincidental, or no way to know?

If I call the plumber/heating company back in, what am I expecting them to do?

I'm wary about calling them because they are costly, and they tend to recommend expensive options.

I have a different small(er) business that services the boiler annually that I probably trust more.

I just want it back to the way it was 3 months.

Any advice would be welcome as well as what level of urgency there is in fixing the issue?

Grallert

I assume it's the boiler relief thats leaking. I see the gauge is at about 30psi. That's the opening pressure of that relief valve. So it looks like the gauge is doing it's job. Could it still be faulty? Yes. but let assume is ok for now. You can drain some pressure off of the boiler, close the make up water valve and see if the pressure goes back up to 30. If it does you'll want to check the expansion tank.

Why was the domestic mixing valve replaced?

digger5150

https://forum.heatinghelp.com/discussion/comment/1899703#Comment_1899703

Sorry, I'm not sure what the make up water valve is or where it is.

The mixing valve was replaced because we were having issues with hot water in the 2nd floor shower, even after replacing the Kohler shower mixing valve.

The plumber traced the potential issue to the existing mixing valve which definitely had some corrosion on it and the temperature gradient just by hand feel before and after the valve was not good.

There is a marked improvement in the hot water in the 2nd floor shower, though we do have that mixing valve turned up to 5 (out of 7) which is higher than the recommended setting of 3. That is to overcome what the plumber thought was the ongoing issue of scaling of the coils, affecting heat efficiency. He recommended an indirect water tank to solve the issue permanently, but the mixing valve swap worked so we decided not to invest further unless the problem becomes acute.

Grallert

There should be a pressure regulating device somewhere. It's not in the picture you posted. If you step back and post another picture with all of the boiler piping someone will liky point out the feed water valve. Could be up near the expansion tank and will be before the pressure regulating device.

rontram

The feed valve is probably clogged with sediment preventing it from closing completely. If you clean it out there's no way to be sure if the problem is fixed until you're sure the pressure is staying low. I find it easier to replace it than try to clean it out.

digger5150

I just realized my original post was incomplete. I copied it in and now it should make more sense. I added a few wider angle shots of the entire system.

EdTheHeaterMan

Sometimes a homeowner is not familliar with the terms we use for the different parts of the heating systyem. maybn times a homeower will call this boiler a furnace incorrectly because it is where the fire is. this would be incorrect for the trade because we call a heationg device connected to ductwork to move hot air a furnace .This heating device is connected to radiators and uses water to move the heat (not air) so we call it a boiler.

Here are the common names we use for parts of a boiler system.

A is the pressure gauge.

B is the operating control. It includes the high limit, the low limit, and the circulator relay.

C is the circulator. It moves the water through the pipes that connect the boiler to the radiators.

D is the burner. This one is an oil burner, but it could also be a gas burner.

E is the primary control, or safety control. Its function is to turn off the burner if the fuel is not producing a flame. We want the burner to stop supplying fuel to a boiler that has no flame because that would be dangerous.

F is the boiler relief valve. It is hidden by the circulator, but its purpose is to make sure the boiler water pressure does not rise above 30 PSI (pounds per square inch). That would be dangerous as well.

G is another relief valve. This one measures both water pressure and water temperature and will release water if either exceeds the valve's safety limit.

H Those are extra chairs for the poker game on Thursday night and have nothing to do with the boiler system.

I is the makeup water system, which is not shown in this photo. This is how the system is filled with water. It is made up of a series of components. From left to right, there is a manual service valve, an automatic fill valve (also known as a pressure-reducing valve), and finally a backflow preventer. The backflow preventer has a copper vent connection coming out of the bottom that may discharge scalding water, so the vent pipe is directed to a safer location.

J is the discharge vent tube shown in both the photograph and Illustration I. If you follow that pipe upward in the photo, out of the frame, it connects to the makeup water section of the boiler—specifically, the backflow preventer.

Hope this helps!

EdTheHeaterMan

Now that classroom learning is over we will move to the lab and have some hands on training:

Three reasons for the relief valve to discharge

1. Defective valve
2. Boiler presure is at or above relief valve setpoint (valve is working properly)
3. Debris is lodged in the valve seat and not closing 100% (may be easy to fix or may be defective). You need to pop the handle to see if you can clear the debris.

Since you pressure gauge is reading close to 30 PSI, I believe your valve is operating as it is supposed to. That being the case you need to find out why the boiler pressure is going to 30 PSI when a normal boiler operating pressure, like your Weil McLain WTGO, would be 12 to 18 PSI.

There are three reasons your pressure may be going to 30 PSI and the relief valve is discharging.

1. The automatic feed valve is defective or set at the wrong pressure. this will allow more water pressure from the household water system to increase the boiler pressure above normal
2. The expansion tank is defective or improperly charged with the wrong amount of air pressure. (That is is covered in the class on expansion tanks that you didn't pay for yet)
3. The tankless coil has a leak that is allowing household water pressure to leak past the coil into the boiler. that will cause the boiler pressure to increase above the normal operating pressure.

Class dismissed

I hope this helps.

EdTheHeaterMan

Extra credit for additional work:

Thanks for the additional photo.

digger5150

Thanks Ed - that is all helpful! I'm guessing a leak in the tankless coil would be a bad outcome(?).

What is the likelihood this is related to the domestic mixing valve swap? Or, is this just coincidental?

I'm asking because I can bring back the plumber who did that work if it's related and they may not charge me for the basic service call (maybe).

What is the urgency of fixing this issue? Can it be addressed within the next month or do I really need to get someone in right away to fix it?

EBEBRATT-Ed

@digger5150

As others have said there are a few things that can cause over pressure. So someone has to troubleshoot this.

That could be you or your plumber. The plumber has to charge $$$ so the smart thing would be for you to eliminate some of the possibilities to keep the plumbers troubleshooting time down.

Could be"

PRV (pressure regulator) feeding boiler is leaking by

Expansion tank could be bad

Tankless coil leaking into boiler water

Bad pressure gauge or relief valve

As others have mentioned since you gauge reads 30 psi and the relief valve opens at 30 psi that PROBABLY eliminates those items as an issue….note probably.

1. Eliminate the boiler prv. Close the valve in the feed water line to the boiler. It's on the back wall with a tag labeled boiler on it. Then drain some water from the boiler slowly to get the pressure from 30psi down to 15psi. Then close the drain. Leave the boiler in normal operation. Check the pressure once in a while. The pressure may go up and down as the boiler heats and cools but should stay in a safe range 10-25psi. If it goes back to 30 and starts dripping that means the feed valve PRV is ok and there is another issue. If it doesn't rise to 30 the PRV IS the issue and it needs to be replaced or cleaned.
2. Eliminate the tankless coil. Let the boiler run as normal. Drain down to 15 psi but keep the boiler feed water valve open. I don't see any valves to isolate the tankless coil so thes may need to be installed to eliminate the coil.
3. Have them check the expansion tank air side pressure. They have to remove the tank from the system to do this. Probably involves draining the system.

If I had to guess #3 would be most likely followed by #1 and then #2

in that order.