Fan speeds up automatically over time

[Mustang]

Hi all- we have a Kozy Z42 with the optional fan kit. When starting a fire I go ahead and turn the fan switch to on but on the slowest speed (fan does t actually come on until firebox gets hot enough, usually around the 20 minute mark). Once the fan turns on and set to the slowest speed you can hear the fan faintly as the RPMs are slow. After the fire has been going for a while the fan RPMs increase automatically even though the fan control is still set for the slowest speed. Is this normal for the controller to increase speed, either with time or possibly heat? We’ve had our unit for a number of years and seems that it has been this way for quite a while, just not sure if it’s a common thing with these variable speed controllers.

 

[stovelark]

Was just reading the manual for your fireplace, it doesn't mention if the fan goes to high speed if the unit is above a certain temp, it only mentions it has a variable speed rheostat. One would assume that the rheostat is changing its resistance internally and might be allowing full voltage through. I'm thinking the only way to test that is replacing the rheostat though... Stay warm.

 

[EatenByLimestone]

How old is it? Could the oil have gone tacky and as it warms up starts to lubricate better?

 

[reaperman1]

I notice this on my blaze king rheotstat fan also. If the fan has been off for a while ( couple of days maybe shorter) its nice and quiet on the lowest setting. Then it becomes louder, not because of a fan issue like you describe, but increased speed on the lowest possible setting.

 

[Mustang]

How old is it? Could the oil have gone tacky and as it warms up starts to lubricate better?

The unit is 11 years old I think. I did replace the fans last year though as 1 wasn’t turning any more but the fan speed changing was prior to replacing

 

[EatenByLimestone]

If the fans are only a year old, it must be on the control side. As mentioned above, the rheostat is a good place to start looking for answers.