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Loose thermocouple = damaged circuit board


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    Customer complaint: older Dunkirk boiler, pilot went out, he removed and cleaned the pilot assembly, reinstalled, lit pilot then observed main burner light. As he was putting covers back on, he jostled the thermocouple line and the pilot went out. Subsequently, after relighting the pilot, the main burner would not light.

    I diagnosed the Hydrolevel 3250 controller as failed and replaced with new, but the same thing happened as I was putting on the covers. Contacted tech support and was told to replace the new controller under warranty. This time I checked and tightened the slightly loose thermocouple into the gas valve. The boiler has worked normally since.   Note: the problem with the failed controllers was at the gas valve relay providing 24v to B1 & B2 on the printed circuit board. How would the loose t-c cause this?

Edited by Freezer man Fran
Simple typo
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44 minutes ago, Freezer man Fran said:

    Customer complaint: older Dunkirk boiler, pilot went out, he removed and cleaned the pilot assembly, reinstalled, lit pilot then observed main burner light. As he was putting covers back on, he jostled the thermocouple line and the pilot went out. Subsequently, after relighting the pilot, the main burner would not light.

    I diagnosed the Hydrolevel 3250 controller as failed and replaced with new, but the same thing happened as I was putting on the covers. Contacted tech support and was told to replace the new controller under warranty. This time I checked and tightened the slightly loose thermocouple into the gas valve. The boiler has worked normally since.   Note: the problem with the failed controllers was at the gas valve relay providing 24v to B1 & B2 on the printed circuit board. How would the loose t-c cause this?

Maybe neither controller was actually defective.  Diagnosing stuff like this with 'black boxes' can be an adventure.

Edited by Marc
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They were defective after these specific events occurred. The integral transformer was still giving 27v on the secondary. The thermostat was stillreceiving 27v and calling for heat. The display was in turn displaying the boiler temp and indicating a call for heat yet was not providing power to the gas valve after the  t- c was "short cycled."

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9 hours ago, Chad Fabry said:

When you're talking 3 milliamps- loose is everything.

Its the circuits with low voltage sources that demand solid connections. Even if its just a milliamp, open that circuit at a connection and the entire voltage of the source is developed there.  Low voltage is easy to stop. Higher voltage, to some extent, will microarc and restore the connection.

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2 hours ago, Marc said:

Its the circuits with low voltage sources that demand solid connections. Even if its just a milliamp, open that circuit at a connection and the entire voltage of the source is developed there.  Low voltage is easy to stop. Higher voltage, to some extent, will microarc and restore the connection.

I'm pretty sure you just said you agree that a loose connection at the thermocouple will affect the operation? 

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