Blower Cycling On-Off ... Thermal Switch

[Islander08]

I have a new BIS Nova fireplace, which seems to be burning fine. It has a built-in blower. Plugged straight into an extension cord at the moment.

The blower works fine and is actually pretty quiet, being mounted in the back of the fireplace.

But when the fireplace gets hot with a fresh load, the blower shuts off. Then comes back on maybe a 1/2 hour later. Seems like a thermal switch cycle, as it is repeatable. On lower burns it runs all the time.

Is this normal?

 

[DAKSY]

Thermo-discs are by default in the "open" position. When they heat up they "close" to complete the electrical circuit.
It may be the amount of air that the blower is pulling past the thermo-disc. I've seen instances where the disc gets cooled down enuff that it'll open up & shut the blower off. Lower speeds tend to move less air & the disc won't cool to the opening temperature...

 

[Corey]

I have seen thermo disks in all sorts of flavors...normally closed - open on rise, normally open, close on rise, etc. Some even have a normally closed and normally open terminal and reverse on heating or cooling. Since the problem is heat related and seems to be repeatable, it does sound like some sort of temp switch issue, but beyond diving into the schematics and tracing where power is supposed to be and when, then comparing that to the actual wiring, it's hard to say where to start. I guess you could look around and see if there is any switch/thermostat with terminals labeled "C" - common, "NC" - normally closed, and "NO" - normally opened. If you find this and "NC" or "NO" has a wire in it, you might try moving that wire to the other terminal. Beyond that, if it's new, this may be a problem for the dealer to tackle.

 

[Islander08]

Thanks for the advice. I've emailed the dealer...

It doesn't appear to be a cooling issue as mentioned with the thermo disk. It only shuts off when the fireplace is good and hot. Seems more like a thermal protection switch for overheating the blower motor.

The problem with troubleshooting is that this fireplace has a louver-less facade, and the fan is located in the back of the enclosure. Only access is by removing the bottom refractory and breaking the factory seal on the sheet metal cover under it. So I haven't "dug" that far into it yet.

I wasn't sure if this is normal behavior for a fireplace blower for safety reasons...sound like not. My old fireplace had a blower, and never did this. However, this BIS Nova gets much hotter, so maybe that's why its needed. I plan to add a variable speed, and that may solve the problem. Although running the blower at max seems like the way to get the most heat from this unit...