Boiler shutting off at 140 but temp control set much higher.

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Hands007

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Boiler burner is only turning on when the boiler temp falls below 125 and staying on until heat is 140. If I fiddle with the boiler temperature knob or the outside reset diff knob it will cause the burner to keep running for a bit longer to a higher temperature but it seems to fall back into it's 125/140 pattern shortly after. We replaced a zone valve recently and it may have had this problem since them but has just not been noticed.
I have:
- removed and cleaned the temp sensor. Temp sensor seems accurate when left out and is reading the same as the actual temperature gauge on the boiler.
- readjusted the boiler temp to max and back (usually keep at 190)
- readjusted the outside temp diff. settings
- shut off and restarted the boiler

In the manual for this boiler and control panel there is a mention of a thermal purge feature where the boiler runs the circulator but does not turn on the burner if the water is above 140. Also, the bypass circulator mixes incoming water that is lower than 140 with warmer water form the boiler. Oddly, both of these settings are 140, the same temperature the boiler keeps shutting the burner off at.
I have read the manual for the boiler and the control and they are both a little lean on details. I think there should be an additional reset or adjustment somewhere. It seems to me it has to be the boiler control but I can't figure out what it could be.
I would love to hear your suggestions, advice
 

Fitter30

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Both operating and reset controls are set at the same temp. Operating should be set higher 180*. The control set at 190* is that the limit?. The reset control most likely be a external control with a water temp sensor and outdoor sensor.
 

Hands007

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Thanks for getting back me. Appreciated!

The boiler seems to be running well at the burners, good flame color and doesn't seem to be any clogged burners.

I do not know what reset controls there are. There are no other point of adjustment that I can see besides the boiler temp and outdoor diff.
Yes, Operating boiler temperature limit is usually set to 180 or 190. The limit is 220. However, it keeps shutting off at 140. The water temp sensor, which seems to be working ok. The outdoor sensor, which I have never really investigated, I lowered it form 25 to about 5. There does not seem to be another manual setting that I can adjust
 

Hands007

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Here is an image of the boiler control. I’ve realized it only turns on the burner after I fiddle with ANY of the knobs while heat is being called for or if boiler temp goes below 125

C5E0A678-B721-473C-A3AB-C7003A40FFD8.jpeg
 

Hands007

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Just to update in case anyone else has this issue. I have not really found a fix because this only shows up on days where the external temp is well below freezing. I suspect it is actually a problem with my smart thermostats turning of the burner and leaving the circulator on to save heating $. Have seen the same problem with my thermostat and someone else's boiler system. Put manual thermostat's on and the problem went away but it is also a warmer day. Thank you for you help!
 
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