Gas boiler pressure too high

[szeik]

I noticed the pressure on our Utica MGB125hd boiler was up around 40 psi. I was concerned because I read that the range for a gas boiler should be between 12 and 30 psi.

I bled one of the radiators and there wasn't any air but I noticed the pressure went down a bit so I let a little more water out from the radiator at the bleeder valve and the pressure went down some more. I probably let out about 10 ounces of water from the system.

It is now running at 27 psi when hot. What would cause the pressure to go up like this?

The boiler is about 20 years old. I asked the manufacturer how long they are supposed to last and they told me 18 years. I am thinking maybe a faulty relief valve somewhere. I would appreciate any thoughts on why this might have happened.

[Dean Hoffman]

I'm not familiar with these systems so don't give a lot of weight to my suggestion. Are you sure the pressure readout is accurate?

[micky]

It should be possible to find any relief valve. Did the manufacturer help about that?

Do you have the manual?

I know this site and it's safe, but are all the manual sites safe from malware? This one has no advertising that I recall. How does it make any money? It doesn't claim to be a public service.

It seems to have 3 copies of the same thing, although they are 1, 2, and

4MB!!!

It says " Cast Iron Gas Fired Boilers For Forced Hot Water" Isn't hot water pressure handled just by a pump, so why woudl bleeding water lower the pressure? I haven't had hot water radiators for 50 years, then I had steam for 12. Steam had a pressure relief but hot water? OTOH, the hot water had barely any pressure at the radiator. Some radiators had to be bled at the start of the heating system, and the water just dribbled out. a three story house. Have they added pressure in the last

50 years. ;-)

[trader_4]

Because it's a closed system, with a one way valve that allows fresh water in but not back out.

[Ed Pawlowski]

There is a valve that adds water as needed. There is also a pressure regulator If they are failing or leaking past you can get over pressure. Not sure what you have but is similar to this

[micky]

So? So why would the wateer pressure be higher than the city water pressure or the pump water pressure?

[Ed Pawlowski]

City pressure is usually in the 45 - 50 psi range. The heating system is closed so when you heat the water pressure goes up. There is a backflow preventer/check valve to retain it in the system. Overall, not much different that industrial boilers. At work we ran them at 125 psi but I know some that run at 300 psi to spin turbines.

[Hal Bundy]

Water expands as you heat it.  Maybe the bladder in the expansion tank has failed?

[Ed Pawlowski]

Yes, there should be one. They do fail too as it is just a rubber bladder.

[szeik]

That's what my plumber said. He is replacing it today. Can anyone tell me what a reasonable price is to replace an expansion tank? I looked up the cost of the tank and it is about $250.

[jimmy]

Here's an expansion tank:

You'll probably get charged for ~2 hours labor.

[Dean Hoffman]

This is obvious but maybe there are a couple things you can do ahead of time to speed the process. I don't know what they might be. Then stay out his way and shut up. I used to do repair irrigation systems. One of the more annoying things was someone telling me how to do something I'd done dozens, maybe hundreds of times before. Some would actually get in the way and "help". It's distracting at the least.

[trader_4]

Some repair shops have a sign:

Labor Rate;

$100/hr $150/hr if you watch $200/hr if you help

[szeik]

LOL!!! He actually likes to talk and doesn't seem to mind me watching. He explains everything to me which I enjoy. I know him outside of the plumbing business so we have other things to talk about.

He was able to replace the expansion tank without draining the system. Lost maybe a half gallon of water when he took the old one off but I was able to bleed out the air and it is working great. Pressure is now 20 PSI when hot.

He told me that from his experience Utica boilers last a long time. That was nice to hear. It was installed in 1999 so about 21 years old now.

Back in business! Thanks again for all the great feedback from all who replied!

[bud--]

So what was actually wrong? What was the problem with the expansion tank?

Not all pressure tanks have a bladder. The air in the tank can then dissolve into the water and go somewhere else (radiators?). May have to drain the expansion tank occasionally. The one I have - valve tank off from the heating system, open the tank drain valve, I think if the screw on the valve handle is removed it allows air into a very small pipe to the top of the tank which allows draining better.)

There is a device on some systems that removes air from the circulating water and sends it to the expansion tank.

Some systems have a valve from the house water system that auto-fills the heating system to a set pressure. There has to be a check valve between the house system and the heating system.

[szeik]

It was filled with water. I think the bladder must have been broken. From the looks of the old expansion tank I think it was older than the boiler. So well over 20 years old.

[Tekkie©]

On Fri, 8 Jan 2021 03:25:44 -0800 (PST), [e-mail] posted for all of us to digest...

The expansion tank may be bad. The bladder inside leaks and the air side becomes waterlogged. Put a pressure gauge to the valve stem it should read 12# or more, there should be a sticker on the tank. It is the usual failure and you may be getting water out of the relief valve. Replace that too. Once they start leaking they will never seal properly again. The last item is the water fill may be stuck open. The tridicator may be bad but until you check the other items first you won't know. Do you have glycol in the system?

Or call for service.

[Tekkie©]

On Fri, 08 Jan 21 14:06:10 UTC, micky posted for all of us to digest...

Because water expands when heated. The system should not be above WAG 25#.

[Tekkie©]

On Sat, 9 Jan 2021 16:45:31 -0600, bud-- posted for all of us to digest...

They are called air scoops and they send the air to the hi-vent which is a little brass can that vents air. The air scoop could never make enough pressure to vent to the expansion tank.

[bud--]

"Air scoop" is one of the types of air separators. They don't all "scoop".

All the houses I have lived in but one are hot water heat. Probably all of them, and the last 2 in particular, had an expansion tank without a bladder - probably was not invented yet. Probably none had an air separator, but if they did the air would go to the expansion tank. Far as I know none had a hi-vent.

In newfangled systems with a bladder tank the air couldn't be sent to the tank - it would be on the wrong side of the bladder.

Don't know what that means.