If you are heating with Propane gas, the term frozen usually applies to the regulator supplying gas vapor from the tank. At the tank there is a small copper tube that connects the tank valve to the regulator. Wrapping a warm damp towel around the regulator near the junction of this tube will usually thaw the tiny ice particles inside withing a minute or two. this will allow the gas to flow to you system. Most gas companies will add methanol to their gas if they are made aware of a situation where the tiny droplets of water vapor are present in the gas.
There is no danger of explosion in thawing this way.

Thank you for the reply. This is a natural gas furnace. I got an idea that didn't work. I used the "Whole House Fan" function and placed an electric heater beside the return. It raised the temperature at the registers from 59 to 68 degrees in 5 hours. But the gas valve is in a separate compartment from that warm air so that wasn't enough heat to thaw it. Meanwhile our 3 electric heaters are getting a workout.

There should not be enough moisture in NG to cause freezing (it decreases the heat output available from the gas).

Why are you repairing a 21 year old furnace ? In a few days it will be 22 years old. Your not being very informative. Is your furnace outside in a closed enviorment
and the heat is ducted into the home ? If so NOT a good idea.

Brickeye, Thanks for that info. I think someone wants to make a few $$ selling a gas valve. I used to maintain my Goodman's myself but I never messed with gas valves and lines.

Kalining: And Sir in a few days I'll be 78 years old. Old things work well if properly maintained and Social Security doesn't add $$ for a new furnace to my check. I only asked advice for the safest way to thaw a frozen gas valve regardless of where it is located but thanks for the reply.

I found the answer: if this kind of dual gas valve/pressure regulator is subjected to moisture, it should be replaced. Here's what I found:

Pressure Regulator
"A typical problem which can develop with natural gas pressure regulators in the winter time is they can freeze up especially when they are at the end of a long gas line run which is open to the outside ambient air temperatures. Natural Gas contains a small amount of moisture (approximately Gas Valve
"The gas valve usually requires no maintenance but if it is ever submerged under water or becomes excessively wet from moisture it is recommended it be replaced and precautions taken to prevent the new gas valve from getting wet."

My Gas Valve/Regulator
"VR8204M-1059
Honeywell gas valve / regulator. 3 - 5", preset @ 3.5" water column. 24 vac, 60 Hz, 0.5 amp. Natural gas. 1/2" NPT in & out. Pilot and main valve control. New, old stock.
Goodman P/N: B12826-07."

So there is the answer. A combination gas valve/pressure regulator can indeed freeze and if so, it should be replaced.

Thanks to all who replied. Problem solved.