Thermostat has no power and pilot light wont light


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Old 03-14-13, 07:45 PM
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Thermostat has no power and pilot light wont light

Hi, we've been dealing with no heat for awhile now (have been subbing our gas fireplace to heat our house), but aren't desperate to buy a new furnace either. What we have:

Goodman furnace 1995 model # GMP075-03
automatic gas ignition system Z21.20
Honeywell thermostat (takes batteries but also connected to furnace for power)

Our story:

Thermostat for the past few months would turn off randomly but would turn on randomly too - I thought this was in response to the temperature being fulfilled in the house until one day it stopped working entirely. Then we noticed our furnace was not lit and no heat was being produced, and we saw the thermostat needs batteries, put them in and voila, it started working but our furnace still refused to light and showed a red light with 4 blinks which prompted us to call an hvac tech. After 1 1/2 hrs he decided that though the 4 blinks indicated a limit switch was incorrect, we needed a new control board because our thermostat has no power either. So we replaced the control board which did nothing, and after re-checking our limit switches, we found the one that was indeed broken, and replaced it, which fixed our blinking red light problem. No more blinking red light. But our ignitor still wont light or get hot, thought that was broken so we got a new ignitor. Thermostat does send messages to furnace though as it will turn on the fan but it wont have power unless it has batteries. Could the gas valve break, and if so how would I know to check it? The gas is on, the valve is open but I don't hear or smell gas when the thermostat is turned up to send the message to the furnace to light the burners. Please help!
 
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Old 03-14-13, 08:40 PM
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Please give us a step by step as to what happens when the thermostat calls for heat.

Ex: inducer fan starts, hot surface ignitor (HSI) glows, gas relay clicks, etc.
 
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Old 03-15-13, 04:05 PM
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A decent tech should be able to figure it out easily. I think you just got a parts changer.
 
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Old 03-15-13, 07:54 PM
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So when I turn the furnace on and set the setting on the thermostat to heat and turn it up above the current room temperature with the fan in the auto setting nothing happens. When I turn the fan in the on setting (on the thermostat) the fan turns on, but nothing happens within the furnace itself. No clicking, no glowing from the HSI, nothing. And again, the red light on the furnace itself is not blinking so nothing to direct me to.
 
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Old 03-15-13, 08:26 PM
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We know that you are getting power to the furnace and that the thermostat works, because the large blower runs.
There is a fuse on the circuit board which, if blown, will keep the normal heat functions from occuring. I would check that and also check to see that all wires were properly attached to the circuit board, since you had it replaced.
 
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Old 03-16-13, 08:01 AM
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Do you have a volt meter and know how to use it?
 
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Old 03-18-13, 07:44 AM
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My best guess based on the information you have provided is simply that the Hvac tech installed the wrong circuit board. And oh my goodness I hope you didn't pay for that circuit board because I would be on the phone with the supervisor getting my money back if it were me.
 
 

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