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Blower and exhaust motor running all the time

938 Views 16 Replies 4 Participants Last post by  ajaye
Hello to all,
Here is my situation.
My thermostat has 2 settings for the blower motor, AUTO and ON.
I always keep the setting on AUTO.
Up to 2 weeks ago, this is what would happen
When there is a demand for heat, the exhaust motor go would go on, the gas heat would go on, and after a delay the blower would go on.
If I would put the thermostat setting on ON, the blower motor would be on all the time circulating air.
Since 2 weeks ago, the blower motor and the exhaust motor stay on all the time even if I put my thermostat to AUTO or even to off completely.
Here is what my system is.

Inter-city products

Honeywell st9120 fan timer board

Durozone sms 2 zone controller.

2 White rodgers 1f80-54 thermostat one wired into the zone controller as a master and one wired as a slave.

Where would I start trouble shooting this issue.

The fact that the blower motor is on all the time is not that great of a problem, but the exhaust motor on all the time is. It gets quite hot and i have a feeling that it will not last very long.
So what I do is, I shut the system down completely for a few hours a day to give the motor some time to cool down.

Can anybody help?
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Is the unit cycling the burners with a call for heat?

Is it heating properly?

Are you sure it's not the high limit cutting off the burners due to overheating?
When there is a call for heat all is fine. Gas burner goes on, stays on till the temperature reaches the pre-set temperature and then goes off. But blower fan and exhaust motor stay on.
Since you're on zoning, try disconnecting the control wires from the zone panel and see if it the motors shut off. rule it out.

you can simulate a cycle by jumping r and w at the board.

control boards can act funny if there's current leakage.
Thanks a bunch 12345a.

I listened to your advice.
Here is what i did.

Shut off power to unit.
Disconnected zone control board.
Applied power to system, nothing happening.
Jumped R and W, blower and exhaust fan come on at the same time, gas valve clicks, pilot comes on, gas valve clicks again, full gas comes on.

As soon as I remove the jumper from R and W, gas goes off, blower and exhaust stay on as long as i don't shut off power to unit.

I am thinking that the timer that controls the fan and exhaust motor may be faulty and is not sending the shut off signal. Also, normally when there is a call for heat the exhaust motor comes on, then the gas comes on, and after a 30 or 60 second delay the main blower comes on.
Now both motors came on at the same time.
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I can't find a schematic to further advise re troubleshooting but chances are the fan timer board is bad.

Does it have a honeywell smart valve? That does communicate with the board with respect to confirming burners are lit, blower timing so it could also be an issue if applicable. It may be difficult to troubleshoot.

Furnaces haven't been sold as inter-city (became international comfort products) for a long time so it's probably old and wise to check the heat exchanger for cracks and popped rings before spending any money on it.
I agree... the relay on the fan timer board probably has fused contacts. Smack it sharply a few times with a screwdriver handle. It may come loose and work until a replacement board csn be had. You can disconnect the wire on the G terminal to confirm that the fan relay is bad... the proof being the fan continues to run with the wire removed.
Thanks to both of you. Your input is greatly appreciated.
It does have a Honeywell smart valve SV9501M2528 that has been installed in April of '19.
I replaced the timer board going with the assumption that the board may be gone. I had a brand new one bought a few years back just in case.
As soon as I put power back to the system, the blower and induction motor went on and do not go off even when the thermostat is switched to off or the thermostat is on and fan to auto and no call for heat.

Attached is the schematic from the system panel.

The status light on the control board is blinking as per normal in the manual

Any idea where I can go from here?


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As soon as I put power back to the system, the blower and induction motor went on and do not go off even when the thermostat is switched to off or the thermostat is on and fan to auto and no call for heat.
Does it still do the same thing without the zone panel connected?
If no, I wonder if the panel is bad.

Try checking voltages at stat terminal trip when this is happening - between C and W, C and G.

See if it behaves normally with the panel connected - simulate call for heat, jump R to W, see if the sequencing (fan delay, etc) is correct.

Thanks for being so quick to reply.
The valve was replaced in April. Would it even make sense that the valve should be the issue?


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Did you put the jumper plug on J1?
What's interesting is, that the zone controller seems to be doing its job properly.
When zone 1 calls for heat and zone 2 does not, the damper for zone 2 will close and damper for zone 1 will stay open. And vice versa when zone 2 calls for heat and zone 1 doesn't.
The furnace control board should behave the same whether you simulate a call for you manually or the panel does it.

For now, focus on verifying the furnace itself is working properly before dealing with the panel.

Leave the zone panel disconnected and see if the it idles with no call for heat and if the fan timing is correct when there's a call.

The valve was replaced in April. Would it even make sense that the valve should be the issue?
Not super likely to be the valve but you never know. I speculated in last post, then edited it out.
The gas valve was replaced in April.
The system has been running perfectly since then till about 2 weeks ago.

J1 is on the valve or the board?

Question on the side, what is the difference between An SV9501M2528 and an SV9501M2056?

I just noticed that the one that was replaced in April is a 2056 and the replacement is a 2528.
I will go through the disconnecting of the zone panel again and do the manual thing, But I need to leave town and will only be back in a week. meanwhile I'll get the wife to shut the system off for a few hours a day till Ii get back.
You will hear back from me when I am back.
J1 is on the valve or the board?
J1 is on the timer board. The jumper plug is required when certain valves are used. You should check the instruction that came with the board or call Honeywell's help desk since there are so many combinations. The plug ordinarily comes with the board. I think it has a jumper wire from pin 1 to pin 6. You can trace the wires on those two pins to see what it might affect.
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I'm a non-prof. but and I don't now if this helps, we used to get this on our old water tank.
It turned out the engineer said it was a common issue , that the water tube (can't remember the proper name) DIP Tube, had dissolved and disintegrated into the tank,
so the full tank was not being heated only the top 3rd, so it was being used up more..

Changing the DIP tube fixed it
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