The furnace in my house (already installed in house before I bought) is a Carrier Weathermaker 58VUA80-101. Don't know if it's 9000 or what.

When called for heat, (1) main blower turns; (2) Inducer motor turns; (3) Pilot flame fires; However main burner doesn't work. After many sparking it stops and give error code 34 (pilot proving fault) then 14 (pilot proving locked). This is repeatable, every time the pilot flame fires but just no main burner fire.

I checked the thermal-couple, it gives about 20mV. Some "Home Fixing" books say any thing above zero means good thermal-couple. During the pilot flame on, I can hear that it still sparks (can see the spark and hear the sound). Some valve might be clicking too (can't tell from motor and spark sound).

Some web articles say this could be the gas valve fault (pilot or main, but I don't see why pilot valve, as it works) or the control board.

How do I measure (with multi-meter or any equipment) the valves to see if they are at fault?

How may volts are those control lines (for pilot or main gas valve, for example)? Can I send a voltage to the valve to see if it works (so I can tell if it's the control board that doesn't sense or send the voltage to the main valve)?

Appreciate your advice.

Thank you in advance.

Apple

This is likely a dirty flame sensor. They become oxidized and need to be cleaned every so often. Code 34 is classic dirty flame sensor. At least that's the first easy thing to try.

If you're up to it, just take out the flame sensor which is attached with a single screw. Using fine steel wool, gently rub off any oxidation or dirt. Replace. Should take only a couple minutes
Post back with results

If you have the 3 wire pilot style then the pilot assembly could also be defective.

See this if this is the correct one for your unit.

http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/58v-1sm.pdf

And this one also

http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/58vua-1si.pdf