House Water Heater Boiler Temperature Gauge Shows Overheating?

HouseWaterHeater

I thought I had a bad temperature gauge because every time the heater turns off, the temperature gauge on the boiler rises significantly from around 150 f to 250 f. All this happens in about a minute after the boiler is turned off by the thermostat. The temperature gauge then slowly decreases with time and by the next time the thermostat calls for heat, the water temperature in the boiler slowly rises from about 60 f to around 150 f and stays that way while the boiler heats the radiators.

I thought it was a bad gauge because the relief valve never tripped and the aquastat is set to turn off the flames at around 160 f.

Well, yesterday someone came to replace the relief valve because it had a very small leak and also the temperature indicator that I thought was bad.

After replacement, I was watching the boiler heat up and when it turned off, the same big increase in temperature happened with this new temperature gauge so I know the indicator was not at fault and is operating correctly.

So this means that the aquastat is not getting a signal to turn off the heat even though the temperature is in the 200 f range? The aquastat is in the same area as the temperature gauge/expansion tank and I think that area of the boiler is "cooler" than the actual temperature in the rest of the system while the system is on.

Something else I noticed was that as soon as the system turns off and the pump stops running, I can hear a lot of water movement as if a big air bubble was moving through the system. This all happens in about 1-2 minutes after shutdown.


1) The expansion tank is also near the area of the temperature gauge and aquastat. Could the expansion tank be over pressurized and push the water around when the water pump turns off? Or possibly push air into the area of the temperature gauge and aquastat? The expansion tank does not seem water logged because I tapped it and can hear different sounds in the top/bottom part.

2) The water pump arrow is pumping away from the boiler and is using the lowest pipe in the boiler. Did someone reverse the flow and should the pump be pumping into the boiler to push the hot water out of the highest pipe and into the area of the thermostat and aquastat?

3) The first time I noticed this temp gauge movement, I installed another temporary gauge in the drain valve to see if I got the same readings. I haven't installed it again after the new temp gauge installation, but I remember the temp by the drain valve not moving after the boiler turns off and stayed around 160 f while the old gauge would move to 220+ after the boiler turned off. The main temperature gauge is on the top right of the boiler. The drain valve temp gauge is in the bottom right section of the boiler.

4) Below is a link of the video. The first two seconds are under normal operation. Then the thermostat stops calling for heat and the boiler turns off. The screeching sound is the flue damper closing, but all the other sounds are water moving through the heating system. You can hear a lot of movement towards the end of the video.
VIDEO:
https://youtu.be/o6qoychEz-0

Here's a coupe of pics of the current set up:
Under normal operation

One minute after turning off











Thanks and happy turkey day!

Jamie Hall

Not really a mystery -- but kind of interesting, all the same. And actually 250 is quite reasonable, locally -- that's the boiler point of water at 15 psi gauge. What is happening is that without much circulation the water is locally heated up by the residual heat in the metal of the boiler.

JUGHNE

Can you post a picture of the pump from the side....sometimes the arrows are confusing.

If it is backwards then you are pulling the water down thru the boiler and out to the return piping. So when the pump shuts off the hottest water just above the burners would migrate up to your therometer.

Was the pump changed recently?

EdTheHeaterMan

The red arrow in your third photo indicated the water flow is reverse. If the pump is actually moving the water in that direction, your problem will be solved by rotating the pump 180° so the water flows in the opposite direction. The top pipe where the aquastat is located is the Goes outa' pipe and the bottom pipe with the pump on it is the goes inta pipe.

I have experiences that same problem on a customer's boiler that took over 2 years to resolve. If anyone is interested, i'll tell you the story.

Mr.Ed

rick in Alaska

Seems like a big air bubble in the boiler would cause that, but not sure. Maybe see if you can bleed any air out from the relief valve, which from the pictures looks like it did not get changed.
Ed. I love hearing stories, so bring it on.
Rick

EdTheHeaterMan

rick in Alaska said:

Seems like a big air bubble in the boiler would cause that, but not sure. Maybe see if you can bleed any air out from the relief valve, which from the pictures looks like it did not get changed.
Ed. I love hearing stories, so bring it on.
Rick

Customer called with noise from the boiler. Arrived to find a Utica boiler with 4 baseboard zones. I tested all the zones and found no noise. (but I did not try the zones individually). Since I found nothing, I asked the customer if they wanted a tune up/maintenance agreement and they agreed. Also had 2 AC systems. Became a good customer. Over the course of the next 2 years, I got call about a noise from the heater that "moaned" all through the house. As you may have noticed I can be a little comical/sarcastic at times. I just told the customer the house must be haunted.

At one point, one of the Taco 007 IFC zone circulators failed and I replaces it. At that time I realized that I installed the circulator in the wrong direction. That's because the original installer of the 4 zone system piped the manifold very close to the basement wall, and also did not leave much room between each circulator. Everything "Just Fit" perfectly, but the circulators were all unable to access the electric junction box cover. So the original installed removed the 4 screws that connect the cartridge to the pump housing on all 4 pumps and rotated them 180° This made junction box covers accessible.

Well, someone must have replaced a circulator before me and made the same mistake without realizing it. If you replace a Taco 007 the way it comes out of the carton, and put the electric box on the same side as the other 3 circulators the pump housing will be pumping in reverse.

I then proceeded to rotate the housing on both the replacement circulator and the existing circulator that was improperly installed years ago. Now that customer calls me "the Ghost Buster".

As long as one or more of the correctly installed zone pumps was operating, the incorrectly installed pump has little consequence, however if only the zone with the wrong direction pump operating, the cold water from the radiators would pass over the aquastat that was located similar to @HouseWaterHeater's aquastat location. (see third photo) That cooler water would allow the boiler temperature to rise well above the kettling point and the moaning and popping would be heard in all the connected piping in every room of the house. As soon as a proper zone called for heat the noise would be gone. Thus making it impossible to find without operating the only the problem zone. To make thing even more difficult, that was a basement zone the was seldom used. The basement was only occupied when the son returned from college at winter and spring break. So the Ghost only arrived at Christmas and Easter. This was quite disconcerting because the customer was Jewish. (of course I had to use that as fodder for my sarcasm)

Thanks for askin' Rick

Mr. Ed
The HolyGhost Buster

EBEBRATT-Ed

@HouseWaterHeater

I would try the relief valve and see if you get air out of it. With both supply and return pipes going in the side there could be a bubble in the top of the boiler.

PC7060

Does anyone have a idea why the flue goes from a 8” to 7” then back up to 10”?  Guessing on flue sizes but the reduction seems odd. 

EdTheHeaterMan

PC7060 said:

Does anyone have a idea why the flue goes from a 8” to 7” then back up to 10”?  Guessing on flue sizes but the reduction seems odd. 

Yes, when the original installer removed the oil boiler and replaced it with the gas boiler, the supply house did not have a 6 x 7 increaser, so they used a 6 x 5 to reduce to match a 5 x 7 to the existing 7" vent pipe in the chimney.

(At least those are the sizes that I see!)

This is called the "what do you expect me to do" hourglass venting design. At least that is the technical term! for that configuration @PC7060

HouseWaterHeater

JUGHNE said:

Can you post a picture of the pump from the side....sometimes the arrows are confusing.

If it is backwards then you are pulling the water down thru the boiler and out to the return piping. So when the pump shuts off the hottest water just above the burners would migrate up to your therometer.

Was the pump changed recently?

The pump was replaced a couple of years ago.

A couple of pictures of current pump:



From what I can tell, the picture is pointing up and away from the boiler.
Thank

pecmsg

The bottom tap is the return!

HouseWaterHeater

rick in Alaska said:

Seems like a big air bubble in the boiler would cause that, but not sure. Maybe see if you can bleed any air out from the relief valve, which from the pictures looks like it did not get changed.
Ed. I love hearing stories, so bring it on.
Rick

The picture is old and I didn't take a picture with the new relief valve. That makes sense because air can sometimes be heard going through the pipes. I'll try to open it for a little to see if air comes out.
Thanks

pecmsg

HouseWaterHeater said:

rick in Alaska said:

Seems like a big air bubble in the boiler would cause that, but not sure. Maybe see if you can bleed any air out from the relief valve, which from the pictures looks like it did not get changed.
Ed. I love hearing stories, so bring it on.
Rick

The picture is old and I didn't take a picture with the new relief valve. That makes sense because air can sometimes be heard going through the pipes. I'll try to open it for a little to see if air comes out.
Thanks

That pump is drawing off the bottom of the boiler!!!

mattmia2

pecmsg said:

HouseWaterHeater said:

rick in Alaska said:

Seems like a big air bubble in the boiler would cause that, but not sure. Maybe see if you can bleed any air out from the relief valve, which from the pictures looks like it did not get changed.
Ed. I love hearing stories, so bring it on.
Rick

The picture is old and I didn't take a picture with the new relief valve. That makes sense because air can sometimes be heard going through the pipes. I'll try to open it for a little to see if air comes out.
Thanks

That pump is drawing off the bottom of the boiler!!!

Unbolt the circulator and flip it over as one of the Eds said. The arrow should point in to the boiler. The way it is now will cause flow and air elimination issues in the boiler. Might need new gaskets.

motoguy128

Yup. Flow is backwards. SO whats happening is after it shuts off, normally you will still get just a little convective/gravity flow as cool water falls and hot water rises this would also normally occur within the boiler. But since the flow is reversed, the water is fighting itself when it shuts down. Internally the hottest metal should be near the coolest water at the bottom of the boiler and would continue to draw more water through even as the pump shuts off.

To make matters so worse, the aquastat is usually located near the top where the hottest water is exiting the boiler, but instead get 10-20F cooler water while running. So as soon as it shuts down it will jump at least 20F plus the metal heats it another 10-20F.

My stema boiler can run a DHW call on its hot water loop and shut off at 150F, but will drift up to 180F within a couple minutes. The temp probe has that much latency, and the metal has absorbed that much heat.

motoguy128

Also 30psi is too high. Even a 3 story house with 40’ from the boiler to the top radiator would only need 20psi. If single story 10psi is plenty. You might turn down the regulator or the relief may be limiting somewhat frequently.

EdTheHeaterMan

So @HouseWaterHeater, it seems that I called it. Someone replaced that circulator some time ago and now you have a safety issue. The aquastat is a limit control, a safety device that does not allow the boiler to overheat. By forcing cooler water from the radiators to keep the aquastat at an artificially low temperature, the water hear the burners can overheat the water and that can cause premature boiler failure, overheating and possible steaming of the water resulting in noise and relief valve release. You need to get this fixes ASAP.




This is the direction the arrow should be pointing

STEVEusaPA

@EdTheHeaterMan flip your picture, you still have it backwards.

JUGHNE

Ed, the problem was obvious to me by reading the first posting. OP stated the pump arrow was pointing down into the lower return of the boiler.

The pictures were requested as sometimes the arrows are showing rotation and not positivity indicative of direction of flow.

The real tell is looking at the back of the pump to follow the flange port to the center of the impeller. The "hump" is connected to the inlet port.

EdTheHeaterMan

Dah, I spent the time to rotate the pump and forgot to rotate the entire picture back... the doctored photo was upside down. This was a test and Steve passed!

BTW, I fixed it... and now... well... it looks like Steve is wrong ...LOL