two questions about two heaters


Old 10-29-03, 06:29 PM
Thread Starter
Join Date: Sep 2001
Location: Philadelphia, PA
Posts: 56
two questions about two heaters

I need some help here. Two questions - the first is my heater:

#1 - I have a gas fired central air in my house that is 6 years old. The A/C work fine all year. The heater acts strange. I have my programmable thermostat set so the temp. drops overnight. In the AM when I want it to warm up from say 65 to 70, the heater runs for 20 minutes then shuts off regardless of whether temp rose to target level. For instance, this morning the stat switched from 64 to 70 at 6:30 but at 6:50 the heat shut off but inside temp. was only 68. The heater will restart but i have to back the stat down below the house temp. then back up again. I have replaced the stat. several times with several different models to no avail. Thoughts?

#2 - My mother has a Janitrol unit similar to mine but about 10 years in age. Her A/C works fine. But her heat does not. When you turn it on, igniter fires the burners but they go out in a few seconds. It looks like it wants to run but something shuts the gas down. Thoughts on this?

Thanks for your help.

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Old 10-30-03, 12:18 AM
rav12's Avatar
Join Date: Oct 2003
Location: California
Posts: 668
#1 sounds strange. First thing to do is to make sure that it is not the thermostat that is causing the problem (although you say you have changed it many times). Fire up the furnace and use a voltmeter to monitor the voltage on the control wires from the thermostat to make sure the call for heat is still present when the furnace stops running.

If this is the case since your a/c is working Im guessing that it may be an intermittent fault on the controller board something like a poor contact or dry joint. As the furnace gets hot the expansion due to heat may cause this. I would suggest opening up the furnace and wiggling the control board and wires and see if you notice any change. Another possibility is a dirty flame sensor. If it is just about operating due to dirt/residue it may give rise to intermittent operation. Try cleaning it with some steel wool.

#2 Sounds like a dirty/inoperative flame sensor. Try cleaning it as suggested above and see if this helps. Ideally the flame sensor should be cleaned annually.
Old 10-30-03, 10:32 AM
Ed Imeduc's Avatar
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389

That #1 sounds to me like a dirty filter ,duct work not right unit to big.Id look and see if it didnt run so long on this pick up in the morning that it went off on high limit cause it got over heated.Its not all the tstat's you have put in. ED
Old 10-30-03, 04:45 PM
hvac4u's Avatar
Join Date: Aug 2001
Location: NW atlanta
Posts: 3,147
i agree, good advice

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