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Steam Boiler Oscillation

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Posted by Patricia Michalski on September 06, 2004 at 11:25:02:

Our steam generating boiler heats our home through 11 radiators has developed a problem connected with the water level controller.
Sometimes, when the boiler level gets low, the low water cut-off goes into an oscillatory mode: turning on the burner for 4 seconds, then off for 4 seconds. This will continue until the boiler has additional water added manually. Then, the system is stabilized and will operate normally for about a week.
This on-off mode of the burner causes exhaust gases to fill the basement.
The water solenoid is OK, as is the electronic circuitry that activates it.
The water level probe in the boiler is clean and uncorroded and the connector to the level controller is good.
The boiler is Peerless Model JOTTW 125WU rated at 129,000BTU/hr. installed 1980's.
Fuel company looked at it, checking the probe and electrical connections, but because of unpredictability
have been unable to catch it in the unstable period.
An indirect fired 40 gal. water heater was added to the system about 2 years ago by the fuel co., it has a built-in heat exchanger coil. It receives hot water from the boiler pumped in by a circulation pump. A thermostatic controller operates the boiler, and the circulation pump.
The system was recently modified by a heating boiler specialist, who installed a water heating coil in the furnace to isolate the boiler water from the water heater, since it was suspected the starting of the circulator pump momentarily lowered the boiler water level at the site of the level probe and caused the system to shut down. Then with the pump shut off, it was thought the boiler water level would come back up and the system would turn back on.
Unfortunately, the instability problem remains the same: Unpredictable 4 second on - 4 second off cycle.

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