flame sense through ground

Del

Unit: 10 year old chimney vented smith cast iron boiler with HSI through a White Rodgers ignition control and flame sense through flame sensor----ground.  Old house, wires (and cut pipes)  everywhere



Checked unit out, it fires, burns for 10-12 seconds then goes out, then goes through ignition sequence over and over but does not lock out.  Seemed strange to me so I did all the obvious, cleaned the flame sensor, replaced flame sensor, checked the gas valve, circulator relay and control.  Checked the wiring, found reversed polarity and corrected that problem. Tried a new ignition control, and unit still did the same thing. Pulled off the thermostat wires and jumped the TT terminials.  Checked for ground, and found the 110V romex wire to the unit had no ground at all.  While checking the other wiring, I turned the emergency boiler switch off, and again checked for voltage at the 110V boiler feed and got 24 volts!  I assumed there were some crossed wires somewhere in the circuit and  I advised the customer to have an electrician run a dedicated circuit with ground back to the boiler, then call us if it still did not fire correctly. My question is:  How did this boiler work for all these years with no ground?  If the control, burner ground and boiler case were all connected with ground wires, would the flame sense control still function even though the 110 feed to the boiler was not grounded? I've seen where old BX cable loses its ground, but this was Romex.  The new white rodgers control I put in has the LED diagnostic feature, and it did not indicate low flame signal so I was a little perplexed by this one.  Obviously, it is not sensing the flame. The control is the type with no L2 terminal, the neutral goes through the HSI and the rest of the board is grounded through the boiler.    Any ideas are much appreciated!  Thanks.           

Tim McElwain

Sounds like you have

a real mess on your hands. The answer is yes it could have been finding a ground somewhere typically through the metal to metal contact on the equipment.



I assume this is using the hot surface igniter to prove flame is that correct or is there a separate sensor?



Why was the ignition control replaced in the first place?



The electrician installing new power feed to the unit may solve the issue so I would definitely press for that to be done.



Some control numbers would help me to further assist you.