Majestic fireplace main burner not coming on

[Azo]

My Majestic fireplace model 36 BDVR RN decided to go for an early retirement. More exactly the main burner does not light. I read some treads related to this type of fireplace and fault but I cannot come to a conclusion.
The pilot is working fine and the voltage looks good for switch in off position only.
I have another identical fireplace in the house that is working fine and I compared the readings.
Switch off:
TPTH (top contact) to TH (bottom contact) = 630 mV for both
TPTH to TP (mid contact) = 630 mV for both
TP to TH = 0 mV for both.
Switch on:
TPTH to TH = 0 mV for both (normal since the switch is on)
TPTH to TP = 280 mV for working one and 0 mV for faulty one.
TP to TH = 250 mV for working one and 0 mV for faulty one.
It looks that the main valve is working. When I turn off the pilot and the thermopile starts cooling down and the voltage drops, at about 300 mV I can hear the characteristic sound of the solenoid.
What went wrong?

 

[xtrordinair]

try leaving the burner switch in the off position and then just place a jumper wire across the top and bottom terminals on the valve .250 should be enough voltage to engage the burner.By doing this you are eliminating any resistance load from the switch and wires.If it lights first check the continuity of the switch circuit .If it checks good you need a thermopile generator.

 

[Azo]

I tried to connect the TPTH (top contact) to TH (bottom contact) with a jumper wire without results (switch disconnected). I cleaned the thermocouple end that is screwed in the control unit but nothing changed. I suppose that the thermocouple should be fine if the pilot is working.
The thermopile may be able to give 630 mV idle, but when connected it may not generate the required current and the voltage drops to zero. Is this the logic behind your recommendation to change the thermopile?

 

[DAKSY]

You said you have no millivolts to the gas valve, with the switch on & taking a reading across TPTH & TP. Change the TP. It's shot.
If the jumper across those terminals works, that's proof.

 

[Azo]

Thank you xtrordinair and DAKSY for advice. TP is not capable to supply the required current to open the solenoid.
I used a variable power supply set on 600 mV. Main burner lights and the voltage readings when switch is ON position is: TPTH to TP = 280 mV and TP to TH = 250 mV. The power supply showed me that required current consumed by the solenoid is 130 mA. The thermopile is not completely dead since if I disconnect the power supply the main burner still lights (not enough power to move it, but enough to hold it).
I cannot find in Canada a parts supplier. It may be a law that only qualified/licensed people can service these units. Can you recommend me a good parts supply store? I saw TP sold between $40 (Amazon.com) and $101(Vermont). I also want to add a fan kit since without a fan the fireplace is just for decor. The other fireplace has a fan and this saved me. Over the weekend it was a power outage in Ontario, over 250,000 houses were left in dark due to freezing rain. I used a small inverter to power the fan and around the fireplace I've got around 75F. Good enough to avoid going to a hotel. Vermont sells the fan for $380...this is quite a rip off.
Thank you one more time.

 

[DAKSY]

Thank you xtrordinair and DAKSY for advice. TP is not capable to supply the required current to open the solenoid.
I used a variable power supply set on 600 mV. Main burner lights and the voltage readings when switch is ON position is: TPTH to TP = 280 mV and TP to TH = 250 mV. The power supply showed me that required current consumed by the solenoid is 130 mA. The thermopile is not completely dead since if I disconnect the power supply the main burner still lights (not enough power to move it, but enough to hold it).
I cannot find in Canada a parts supplier. It may be a law that only qualified/licensed people can service these units. Can you recommend me a good parts supply store? I saw TP sold between $40 (Amazon.com) and $101(Vermont). I also want to add a fan kit since without a fan the fireplace is just for decor. The other fireplace has a fan and this saved me. Over the weekend it was a power outage in Ontario, over 250,000 houses were left in dark due to freezing rain. I used a small inverter to power the fan and around the fireplace I've got around 75F. Good enough to avoid going to a hotel. Vermont sells the fan for $380...this is quite a rip off.
Thank you one more time.

Check a local hardware store or heating supply place. Sometimes they're called millivolt generators...$40 - $50 USD is about right...