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Gas Heat will not shut off

I have an old Carrier (I have been told in the past that it's a 30+ year old commercial unit) about 4 Ton A/C- Gas heater that works great, except that once it turns on, it will not shut off, the thermostat has no control of it after turning it on at the preset temperature. I have to turn off the Gas Valve and after a while the blower turns off. Than I turn the Gas back on and when I need heat I turn it on via the Thermostat. When the house gets up to roasting, I turn the thermostat and the Gas Valve off and start over again. I have a Honeywell electronic setback timer thermostat that seems to be working OK. Can anyone help me?

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Either your t stat is failing to recognize the high temp its achieved ,or the gas valve is sticking open despite no low volts to it= very bad. check for 24 volts at the gas valve after temp is way up past stat setting if you have 24 volts to valve the stats bad. if you have no volts to gas valve and valve is still open and burners burning, then the gas valve is bad. if valve has no power to it and is still on , heating try gently tapping side of valve. if it shuts off burners it was definitely stuck. i am not going to tell you you need a new modern system, because i think you already know that deep down inside .so much has changed as far as efficiency, gas consumption ,electric. not to mention the 5 and ten year warranties on most new stuff we sell here. with the economy so slow its a great time to name your price on new stuff. did you know some of the new stuff uses a third the electric in cooling the old units did? and the gov says in 2010 r22 freon will be mandated out of production so gas prices will be 40 dollars a pound by summer of 2009. new filter systems have one filter that last a year and cost 45 dollars and filters down to 3 microns? never clean ducts , coils, ever! wow. get a free est from a good reputable contractor. i think you'll be amazed. est should be free by the way. good luck, i myself like keeping those old ones going but there comes a time for all to go to the bone yard.

Posted on Nov 13, 2008

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