I have a Laars LT400P heater and when I turn it on, the fan comes on, then I can see the igniter glowing but the heater never fires up. I checked the voltage to the valve and it is getting 28 volts (should be 24). If the igniter is glowing, should all the other safety switches be satisfied and then the valve should open? Or are there other checks (safety) that I need to look at?