31yo Bryant boiler intermittent kettling

MinnesotaGuy

On Jan 23 our boiler started banging very loudly at about 2:30 am.

I shut it off, opened the pressure relief valve and let a a few quarts of water and steam out, added some more fresh water back up to about 15psi, hit the switch and it was quiet as normal, for about seven weeks.

Then early this morning it started banging again, and I repeated the same process, and once again it is hush quiet again.

Over the years I might add a few pints of water when I bleed the radiators in the fall. But it is basically a sealed system.

Does it sound like scale and hotspots in the heat exchanger? And why so intermittent?

Is it worth just replacing the heat exchanger, or should I go the whole way and replace the entire unit?

HVACNUT

Please remove the price as money is not discussed here. 
What model boiler?
Can you post some pics from about ten feet away?
Assuming it's a monoflo system if you bleed rads. It shouldn't be necessary if its piped correctly. 

MinnesotaGuy

Jamie Hall

" let a a few quarts of water and steam" Steam, really? Leads me to wonder if the high limit aquastat -- I assume there is one on there somewhere -- is misbehaving intermittently.

MinnesotaGuy

Yes there was actual steam in the heat exchanger. And when it would puff out through the overflow when I opened it, it stopped the noise problem. I'm just wondering why it flashes to steam in there. I think there's something called hot spots from scale build up.

Jamie Hall

Well, indeed it's quite possible that there is enough scaling to create hot spots. After 31 years... there are chemicals which can be used to remove some or all of the scale -- other may chime in with what they use for that. That certainly could -- and should -- be done, particularly if it's never been done before.

However, I'd also want to check that the high limit aquastat is, in fact, shutting off the boiler.

SuperTech

I agree that the aquastat should be the first thing to check. If the temperature gauge on the boiler still functions I would check the temperature on that against what the high limit is set to.  I wouldn't be surprised one bit if the original aquastat on that boiler is no longer shutting down the burners when it should.  A hydronic boiler shouldn't be literally boiling water.  

MinnesotaGuy

I've checked the temperature when it's doing it and it's only about 200. And the pressure is still at about 15 or 16 psi.

The thing is, why would it only do it once and when I started again it just fine for 7 weeks? And when I went down there and it was doing it the temperature wasn't exceedingly high.

So I'm beginning to think it's some sort of an insulating scale problem or a plugging problem in the heat exchanger where water gets caught in an area and gets overheated because it doesn't move through fast enough

bucksnort

What's your high limit set at? What are your supply line temps when it's running? Your gauge, aquaset or setting could be bad.

Jamie Hall

200 gives you precious little margin to allow for hot spots -- or a sticking aquastat. In fact, I would say it's too high -- 180 would be more like it. As @bucksnort said, what is the high limit aquastat set at?

You enquire why it would be just fine or seven weeks and then do it again. And why not? If the aquastat -- or example -- is going bad, that's just what it would do. Now and again it simply wouldn't open when it was supposed to.

EBEBRATT-Ed

@MinnesotaGuy

You aquastat could be out of wack. After 31years it could be bad or have muck around the aquastat well. I would have it changed. And set it to 180 or 190

MinnesotaGuy

Aquastat is at 180.

During the kettling episodes the temp gauge is right at 200, as it is during normal cycles.

Jamie Hall

The aquastat is set at 180. The temperature gauge is right at 200.

Um...

The aquastat is lying to you. Change it.

MinnesotaGuy

Actually the Aquastat could be near 200. But the temp is not boiling.

I get this stuff. Thanks.

bucksnort

The boiling point of water at 12lbs. pressure is 250 degrees. So if you have "steam" something isn't registering correctly.

HVACNUT

I think the OP is confusing water vapor as steam. Of course when he pops the relief valve at 180 or 200 degrees, there's gonna be some "steam". 
The aquastat could be faulty or the tridicator could be faulty. 
What's the water content of the boiler? The water side of the HX could be obstructed in some spots. Try Sentinel X800 or similar cleaning agent then follow up with an inhibitor. 

MinnesotaGuy

Because we are now retired and a couple times a year leave our home unattended while we go on motorhome trips for maybe 4 weeks We need to have an absolutely reliable heating system so we'll probably replace this 31-year-old boiler.

When I came down the basement stairs when it was banging I could smell a steamy smell in the air before I turned it off and released some pressure from the pressure valve.

But oddly, I noticed that it said it was only about 16 lbs pressure when I was smelling that in the air. And that would not be enough to pop the pressure valve. Of course I could easily release The pressure relief myself by lifting the lever slightly.

EBEBRATT-Ed

@MinnesotaGuy

Relief valve are not an operating control so the pressure they releve at and reset at can vary. If it let go at 30 and let some water out it could have been down to 16 when you got there

bucksnort

If your relief valve is popping at what your gauge is saying 16 lbs. your gauge and relief valve could be both bad. You really shouldn't use the relief valve as a valve. the seat in the PRV might not reseat correctly. Think of it as a one time fuse. We really need to know the supply temps right off the boiler. Do you have an infrared thermometer to accurately measure the real temps? Steam and hot water vapor hitting colder air temps is not steam. Think of it as being able to see your breath at 20 degrees and not at 80.
"Aquastat is at 180.

During the kettling episodes the temp gauge is right at 200, as it is during normal cycles".
If you aquastat is set at 180 you shouldn't see 200.

MinnesotaGuy

bucksnort said:

If your relief valve is popping at what your gauge is saying 16 lbs. your gauge and relief valve could be both bad. You really shouldn't use the relief valve as a valve. the seat in the PRV might not reseat correctly. Think of it as a one time fuse. We really need to know the supply temps right off the boiler. Do you have an infrared thermometer to accurately measure the real temps? Steam and hot water vapor hitting colder air temps is not steam. Think of it as being able to see your breath at 20 degrees and not at 80.
"Aquastat is at 180.

During the kettling episodes the temp gauge is right at 200, as it is during normal cycles".
If you aquastat is set at 180 you shouldn't see 200.

Thanks for the info!

WHen this just happened, I came down the basement stairs and could smell a steamy smell. The boiler was banging hard, and the pressure gauge said 16lbs and the temp was at 200.

I turned off the boiler and then opened the pressure relief vale a little bit, as I had done seven weeks ago. Then I SLOWLY tricked in some water to bring the system pressure back up to 15psi.

I understand I should no longer use the pressure relief valve that way. Point taken.

I should use the drain valve with the hose on it. Unfortunately I don't know if I can turn it, because the guy who installed the water heater pushed the heater right up into the valve even denting in the outed sheet metal of the water heater.

Anyway, at 31 years I want peace of mind while we are away for several weeks in the colder weather, and I think we'll just have the boiler replaced.

I can check the supply out of the HX with an infrared thermometer just to see if the temp gauge is correct.


Thanks for your information.

SuperTech

I would also confirm that the gauge is actually working. Isolate the boiler and drain enough water out of it to bring the pressure to zero. See if the gauge confirms this. Just because the boiler is old doesn't mean it needs to be replaced.  Installing new aquastats, pressure relief valves and other parts is just routine maintenance.  

MinnesotaGuy

We require peace of mind. If the HVAC tech could guarantee that the system would be fine while we are gone for weeks, I would consider repairs. But 31 years is two times the currently quoted life expectancy.

Also our distant radiators were not getting hot in this year's -20 below cold snap, even though none gave air at the bleed valves.

HVACNUT

Consider installing an indirect water heater as well and get rid of the gas fired water heater.