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 12/29/2012 11:31 PM

Hi, my furnace (Hydroflame 8525-iV) started running all the time, blower and propane heat. I can't shut it off with the thermostat. This is what I've tried so far:

1) Replaced igniter control board. I did this since I thought it was the thermal relay (not high temp relay) and my wiring diagram doesn't show the thermal relay anywhere and I could see a relay on the igniter control board. No change.

2) I tried disconnecting all the wires on the thermostat and no change. I could sense voltage on the Furnace wire even when it was disconnected from the thermostat. Even if the fan wires had no voltage on them the blower kept blowing.

I don't know what to try next... any ideas?

Thanks, Jeff

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 12/30/2012 1:01 PM

Well, I don't know much. But what I would do first is shut off the propane and elec power source. Then turn them back on, propane first. If it starts up without you doing anything else, you've got a switch problem somewhere.

Every Day is Saturday funner travelin, Ebs,Donna & Beezer the Beast & Buffy the Bitch
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 12/31/2012 6:17 PM
 Modified By RVA  on 1/1/2013 1:34:47 PM

Jeff - Below is a page from one of my manuals that discusses Burner Shutoff Failure. You've already eliminated the thermostat as the culprit, which suggests checklist item #4. Before concentrating on the gas valve, however, I'd perform one more simple test to make sure the thermostat cable isn't shorted. With all power off, remove the wires from the thermostat (there are probably only 2) and use an ohmmeter to check for continuity between the two. If you get any ohmmeter reading (continuity) it suggests those wires are probably shorted somewhere between the thermostat and the gas valve or the circuit board. Good luck. - Dave

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 1/1/2013 6:06 PM

Hi Dave,

Thanks for the information. I wasn't able to get rid of the voltage to the wires going to the thermostat. I shut off the furnace with its combo on/off circuit breaker and pulled the fuse for the Furnace and still was getting the same voltage on the wires. Here's a picture of a thermostat like mine with the same wire colors:

For each wire I measured:

Red : +7.5 = 7.5V

Yellow: COOL = 7.9V

White: FURN = 10.4V

Blue: Hi FAN = 10.4V

Orange: FAN = 10.4V

Green: GND = Common I measured to.

Since I wasn't able to get the voltage off the resistance measurements were screwy but it definitely shows a short somewhere from what I see.

The part where I'm at now and am confused about is where those small gauge wires to the thermostat go? They go into the wall and yet if I look in the box where the furnace control board and valve and blower motor are all I see are large gauge wires and same is true in the power distribution box. Wondering if I need to start tearing the walls apart to trace the wiring.

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 1/1/2013 8:33 PM
 Modified By RVA  on 1/2/2013 1:00:42 PM

Jeff - Below is a link to the service manual for your 85 IV series furnace. Unfortunately, it discusses blowers that won't shut off, but not burners. You'll notice the cover letter also mentions a new position for the blower relay. It appears that this relay, that makes power available to the blower, is either stuck closed or getting it's triggering power from some place other than the thermostat (a short?).

BTW - Aside from getting meaningless readings, an ohmmeter should not be connected to hot wires. Some ohmmeters can be damaged when connected to power while others have built in protection. If yours no longer reads resistance, look for a blown fuse inside. Please let us know how this turns out. Good luck - Dave


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 2/13/2013 2:03 AM
 Modified By Jeff  on 2/13/2013 2:05:09 AM

hi, thanks all for your help. I found the problem. It was a poor original wiring job. The picture below shows a number of wires that are wire-nutted together in different groups. This whole bundle was wrapped together by electrical tape. Apparently the two bare (unbelievable poor workmanship) wires are the ones that cause it to start. Only guess I can think of is that the vibration of traveling caused them to touch. Phew!

Thanks for your help! Just wanted to circle back to close the issue with what solved it.

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