The case of the tripped limit controls, this Friday's case.

RayWohlfarth

The customer called and said the boiler kept tripping the manual reset high temperature limit. I asked what the boiler temperature was and he told me it at 220 degrees, the setting on the limit control. I told him I would contact the factory for a new operating temperature control and suggested he switch the lead boiler. A few hours later, he called again and said the other boiler was doing the same thing. This was like many other systems I sold, two boilers piped primary secondary. The only difference is the engineer specified an isolation valve for each boiler to meet the code requirements for the International Energy Conservation Code
As usual, I will not give any more clues until Friday at 6am EST when the video comes out.

JUGHNE

I think that your last paragraph with the red arrow explains it.

With only one boiler on line the flow is cut down.

The auto valve is in the wrong place?

EBEBRATT-Ed

The boiler shuts off and then the flow reduces and the hi limit trips on residual heat. operating control cant shut the boiler dow because its already off

RayWohlfarth

@JUGHNE and @EBEBRATT-Ed You are both right. It was on this job that I learned that boilers will still heat after the burner is off I suggested a time delay relay which would wait for 10-15 minutes to shut off after the burner did. Thank you sirs. Here is the link to the video
https://www.youtube.com/watch?v=CvRxCrPwFWI

EBEBRATT-Ed

Very common problem if you shut the burner and the pump down or close an isolation valve at the same time