I am trying to diagnose a problem with an old furnace. I have some pictures to help clarify what I have, a ThermoPILE system.

The problem is that the PILOT flame is on, but the main burner does not always light.

I cleaned all electrical contacts today with sandpaper, and made sure they were all tight.

I also made sure the PILOT line and BLEED line were not blocked. (Took them off and blew through them).

I also took out the THERMOPILE sensor, and cleaned it off with steel wool.

And this is a repeat , but I am trying to show that there is a steel connection(steel plate) between RED(Thermopile,pos) to TH1(thermostat,pos).

Also a steel connection(steel plate) between TH2(thermostat,neg) to L2(LIMIT switch, pos):

I was trying to use the "MILLIVOLT TROUBLESHOOTING CHART", on page 2 of this diagram:

But I'm not sure what connections to put my meter across.

For example, the chart says in TEST-A, to test across TP and TH for more than 100mV, with the thermostat contacts CLOSED. (On my gas valve, would that be RED to TH1, or RED to TH2, or something else?)

For example, the chart also says in TEST-B to test from TH/TP to TP for greater than 325mV, with the thermostat contacts OPEN. (On my gas valve, would that be TH1 to WHITE, or TH1 to RED, or something else?)

Also, when it says thermostat contacts CLOSED - does that mean with the thermostat temperature set to higher than the room temperature?

I attempted to do TEST-A, with thermostat set to turn furnace on(I assume that what what they meant by thermostat connections CLOSED?) and measured:
RED to TH2 = 123mV
WHITE to TH1 = 387mV
TH1 to TH2 = 20mV
RED to WHITE = 400mV
L1 to L2 = 26mV

For some reason I did not measure RED to TH1, or WHITE to TH2. Should I have?

Also, those readings were what actually displayed on my meter, when the dial was on the 2000mV range, and the 200mV range.

So I think I'm reporting the voltages correctly? That is, if the meter displayed 123 on either of the ranges(2000mV, or 200mV) - that means I measured 123 Millivolts?

If the gas valve is sticking, can this be disassembled and cleaned? Can it just be replaced?