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Old 10-26-2009, 08:01 PM   #1
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Olsen Furnace - No Heat

I have an Olsen Gas Furnace that was installed in 1995.
Here are the specs:
Info plate inside states DMO FURNACE
Model # HHS90M
WhiteRodgers Controller

A few days ago furnace was staying on but no heat, has worked earlier this season.

The Controller in the furnace has a red light that was flashing 4 times.
The key on the controller states that 4 flashes -- OPEN HIGH LIMIT SWITCH.

My question is - what is a high limit switch and where do I find it.

I also welcome anyother troubleshooting advice.



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Old 10-26-2009, 10:26 PM   #2
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CaptnD - The high limit switch is a temperature activated safety switch that prevents the furnace from overheating. If it gets too hot inside the furnace the switch will open, breaking the circuit allowing the fan to run until the furnace cools down. Once the switch cools it should close again closing the circuit and allowing the furnace to relight. If you switch is open it is fooling the system into thinking the furnace is still too hot. you need to find out what temp rating that switch is in order to replace it.


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