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Boiler high limit tripping

Check that your heat exchanger isn’t sooted up. Use a mirror to look up through the burners while it’s fired up and look for glowing areas of the exchanger.

Check that your circulating pump has good flow. You can do that by feeling what kind of pressure it puts on your flow switch. It’s should be strong. Also make sure that the pump continues to run for a while (usually like 8-10 minutes) after the boiler reaches temp and shuts the flame off.

What temp is your aquastat set to?
 
Occasionally (maybe once a year), my Raypak high limit will also trip. Every time this has happened, there were HUGE winds blowing outside.

It's possible that high winds are blowing so strong....that the flue is not drafting properly....and bang, things get hot, and the safety pops.

Has your issue occurred during windy times?
 
We have only owned the wash for about five months so I'm not sure when it was cleaned last. It was very windy yesterday when it tripped. Maybe that's it.
 
I had the same exact issue two different years and after trying everything, turned out it was just very dirty. A good cleaning and works great. I have the same boiler.
 
This is now happening about once per week but the last three times it did not pop the high limit. It just sits there like it does when it is up to temp with no obvious reason why. To get it working again it takes me turning it off and back on several times (sometimes waiting while it is off) and then it fires up. Is there a specific time to wait to let it rest itself? I'm just trying to figure out how to get it working quicker when it kicks out. I did have a HVAC friend take a quick look and suggested to clean the flame sensor but I'll need to wait for a rainy day that I don't have a more pressing project. Also can someone explain how to clean the heat exchanger?
 
Clean the lighter area. Probably some gunk on top of it. Usually we take a screwdriver and poke the soot out from around it and the problem goes away.
 
Just got my replacement circulation pump which is my problem. The pump was still trying to function but wasn't moving enough water. If its a taco pump it has an oil port. You can sometime get it to limp along if you oil it.
 
Update: I have been limping along and restarting the boiler when it trips out. No time to really go through the boiler right now. I'll update you when I get time to try some of the great advice you all have given us. Thanks for your help!
 
OurTown,

Based on past experience with some similar in design Hydrotherm ... I would ask some local professional duct vacuuming outfits ... get an estimate for them doing it ... with possibly more specialized suction equipment. I was really surprised with some those of those similar small boilers working great after letting a local do it. The plumbers had seen the problem before & referred us to the duct cleaners. No regrets for an extra thorough complete job.
 
Finally I think we are getting somewhere. Our circulation pump motor was stuck the other day. I could hear it buzz but was not turning. After removing it from the pump and checking it I realized the motor spins freely. With the motor off the pump and the boiler turned back on it just sits there buzzing. If you give it a spin it by hand it spins right up to speed. I mounted it back on the pump and it does the same thing but as soon as you spin it up by hand it cranks up to speed and boiler fires right up. It is a Taco Red Baron setup with an Emerson 115 volt motor.
 
but I

Not a motor guy(especially single phase) check the start capacitor if you can get to it.

Best price I found on replacement pump was a zoro with discount, but it was backordered a while.
 
I can't find a capacitor anywhere on the motor. I called a motor shop and he said it might be in the controls somewhere. Could this be the motor timer circuit board going out? They are calling for rain tomorrow so I might take the motor to the motor shop to have it bench tested.
 
OurTown said:
I can't find a capacitor anywhere on the motor. I called a motor shop and he said it might be in the controls somewhere. Could this be the motor timer circuit board going out? They are calling for rain tomorrow so I might take the motor to the motor shop to have it bench tested.
Click to expand...

Doubtful, just see if you are getting 115V to the motor. If it's not running most likely the problem is in the motor
 
I took it to a very reputable local motor shop to have it bench tested. It failed to start for them but said they could probably repair it. The next day they said that the bearings are bad and because they are special sleeve bearings it is cost prohibitive to repair. A new Taco motor is $364 and the whole motor/pump assembly is $367 from them. WTH? I'm no expert but the bearings do not seem bad to me. It doesn't make any noise when it is running and it spins freely when you spin it by hand. The only noticeable issue is some end play in the shaft. I think that is the reason the start windings are not being contacted. After taking it apart again I made a shim to put on the shaft to take up the play. The motor seems to work fine for now after running it through two water heating cycles. At least we know the boiler problem is in the water circulation motor. The reason for not buying a new one right now is that in a few months we might go with two tankless water heaters to make some space for equipment for our new auto.
 
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