I have a boiler type of furnace in my home. When it gets colder the boiler makes a "whining" noise when the gas/pilot comes on to heat up the tank. The noise stops as soon as the gas shuts off. Is this a gas regulator that is going bad? If so, could it go bad quickly altogether and effectively shut down the boiler? What do they cost and how hard are they to replace?

There are many different arrangements of gas controls and regulators when it comes to boilers. If possible, post a pic of yours to help with identifying what you have there.

Type of gas? Propane or natural?

Brand and Exact model number of boiler.

It is natural gas. Model is a AOSmith Hydronic Boiler Model # HW12OP720.

http://pictures.sprintpcs.com/mmps/002_1433a93745669670_1/2.jpg?

I show no AO Smith boiler with that model number but here is what you can do to isloate the problem. Use a non conductive device and place it on the suspected component on your boiler ie the pressure regulator/gas valve. Then place your ear to the device and have someone turn the boiler on. This way you can hear and isloate the problem and make the repairs if necesary.

That model number is right off of the boiler itself. It is about 15-20 years old if that helps

Here is there web site search for yourself. Did you try to isloate the problem like suggested?

A.O. Smith (http://www.aosmith.com/)

Sometimes you try and help people but they are just to ignorant to find there correct model number. What a waste of time on my part.