Hi
Our gas dryer won't heat so I tested all the fuses etc, put in a new ignitor and still no heat. I pulled the connector going from the power source directly to the new ignitor, tested and it shows 120 volts. When I plug that into the ignitor though it doesn't heat up. The dryer plugs into a regular 110 outlet so it I guess the ignitor doesn't need 220 volts to glow. I see there is a flame sensor that could be bad but since I have power to the ignitor it should work. I took the new ignitor back and they tested it and found it good. Any ideas? Thanks.

You said you checked voltage with igniter disconnected, not sensor disconnected. Dirty contacts on the flame sensor can cause the igniter to not function as there would be a large voltage drop across the sensor contacts. With igniter disconnected, there is no load on the sensor contacts and you would read full line voltage. Should have checked igniter voltage with igniter plugged in.

Eric

I really don't want to try to explain the electrical theory involved. The only way you can get 120 volts across the igniter is if the flame sensor is closed. With the flame sensor open (or disconnected), the igniter is now in series with the secondary gas valve solenoid coil. This will cause the voltage across the igniter to be very low. If you disconnect the igniter, if flame sensor is open, the voltage across the igniter wires will go up to around 30vac due to primary valve assist coil and secondary valve coil now being in series. If flame sensor contacts are dirty, that creates a whole other scenario. This is why you need to check things connected and under load. Simple continuity checks can fool you because you are only using the low voltage and current of your multimeter for testing but in actual operation, the devices you are checking are passing much higher current. Dirty contacts can read perfectly fine with basic static multimeter continuity check but can break down under normal load conditions. If you were getting 120vac across igniter wires with igniter disconnected, something must not have been connected properly with regard to the coils or the flame sensor contacts are faulty.

Eric

Assuming the flame sensor contacts are good. If they are dirty creating resistance, then with igniter disconnected, you could read near normal voltage but with igniter connected, it could drop significantly due to voltage drop through the dirty contacts.

Eric

Not exactly. Voltage is just a potential difference. It isn't "drawn" through a circuit, current is. You have to understand the relationship between voltage, current and resistance and in AC circuits, impedance, which is a combination of resistance, inductive reactance and capacitive reactance. Current through a resistance causes a voltage drop. With a load on the circuit (igniter connected) current is drawn and there will be a voltage drop due to current through any resistance (dirty contacts). With igniter disconnected, there is no current draw (or minimal draw through solenoid coil) and thus, no voltage drop. If I create a series circuit using two 60 ohm resistors placed across the 120 volt line (L1 and neutral), the circuit will draw 1 amp and I will read 60 volts between the junction of the resistors and neutral. If I disconnect neutral from the end of the resistor, I will now read 120 volts between junction of resistors and neutral because now there is no current flow and thus no voltage drop across either resistor. I will read the same 120 volts at either end of either resistor with respect to neutral because there is no current flow.

Eric