My main burner is lighting, but only staying a short blue flame. It will not increase with adjusting the thermostat, which I've tested and even replaced... or any knobs under the panel. It just lights from the pilot and stays a small blue flame across both sides. Any ideas? How would I test the gas pressure and/or if its low, how would I increase it? Is something not opening up fully say the main gas valve? It worked 8 months ago last winter.

Gas pressure testing requires a tool see link

http://www.uniweld.com/catalog/gauges_thermometers/gas_pressure_test_kit.htm

There are different types of meters and guages this is only on example.

You connect the meter or gauge with an adapter that fits on the gas valve,valve train pipe line or other area that needs to be tested. There are taps for this adapter with plugs depending upon the area to be tested. Then you have to look at the furnace ID plate to find out if the pressure is at the design rate.

Your problem could be lack of gas pressure at the source since the gas pressure controls on a furnace DO NOT change by themselves and it is very rare that they go bad. Before I would mess with the pressure controls at the furnace I would check to make sure the gas supply is turned on and that it is supplying gas to the furnace. Then if all that checks out you may want to see if the pressure regulator on the furnace is at fault.

Many times a utility company will check the gas line pressure for you for free as a service. If it is LP gas call the LP/Propane gas company for assistance.

There are many different locations on the gas valve/pressure regulator for adjusting the gas. Since there are over 500 different style valves it is impossible to tell you where yours is exactly located.

I normally do not recommend a homeowner test,presssure check or try to adjust the gas flow. Especially on LP/propane gas.

Thanks for your reply. Is the pressure regulator hard to change if that does happen to be the problem? I will look into getting pressure tested but I can say that the main source the valve is opened up parallel with the pipe... I can't open it any higher. I really need some type of schematic to show me the steps of how a furnace works.

Er I mean gas fireplace. Sorry :)

Standard mechanical skills to change the regulator if it is a separate item. Many times the regulator is combined with the valve. Remember to use pipe dope on all pipe fittings.

Just wondering if you know how much it would cost "roughly" if I had to change the whole valve if it is a combined assembly. I called 2 companies yesterday and they want $90 to make service call, plus taxes of course, then extra for parts.

I must second what hvac1000 has said, especially with propane. This really isn't a DIYer job. Save your energies and money for other DIYer projects where the risk-reward ratio is better in your favor. I know money is tight for many folks these days, but you won't think that way if you make a mistake.

I appreciate the risk involved... I totally get that. What I'm wondering is.. in theory, the thermopile and thermocouple 'must' be working at 100% if the burner is at least lighting up a small blue flame across?

The small blue flame all across the entire burner would usually indicate that the gas valve to the burner is opening BUT

We do not know for sure if the valve is opening all the way as in a defective valve.

We do not know for sure if it is a gas pressure problem alone or something else working in tandom to cause the problem.

We do not know the exact voltage being applied to the gas valve during operation and if the voltage is within spec. for the valve to operate correctly.

Hey guys. My friend and I found a spider web had blocked basically 99% of the pipe feeding the main burner. Gave everything a good cleaning, put it all back together and voilà works perfectly! Thanks again for your help and fast responses. Much appreciated!

A prime example of why not to overlook the simple solutions. Glad you got it working.

That does happen. Glad you got it working.

Thanks again gentlemen.