Monitor GF 12 Propane Heater Fan Won't Turn On

[LarryLeveen]

A small coaxially vented propane heater has power, will "click on" when the control knob is turned to "Run." The burner is working properly (gas is turned on and a full flame seen through the viewing window), but the fan never turns on. I _think_ I even hear a faint click after a minute or so -- perhaps the unit trying to energize the fan motor. But the fan never runs. Instead, after a few minutes of the burner running, the unit shuts down, which I figure is the overheat protection sensor doing its job. The unit definitely gets very hot, that's for sure.

So, it seems like maybe there is a bad blower relay or some other fan controller device, or the fan itself is dead. Can anyone suggest HOW I would go about diagnosing what is wrong. The articles online that I see aren't very helpful when they say "check the relay or voltage from the board. If no voltage is recorded, you will have to replace the board or the relay." I don't really know HOW to check the voltage (or continuity). I do have a (fairly crappy) multimeter, so some assistance in troubleshooting would be appreciated.

I haven't opened the unit yet. Thanks in advance.

 

[Dana]

Nobody is going to talk you through a potentially lethal or dangerous procedure until you at least master some of the basics of how to use a multimeter.

Most heaters have an over-temperature shut off for the burner if the fan isn't blowing. If this one doesn't or the over-temp function isn't working, don't let it get so hot that it burns the house down.

 

[Sponsor]

 

[LarryLeveen]

Nobody is going to talk you through a potentially lethal or dangerous procedure until you at least master some of the basics of how to use a multimeter.

Most heaters have an over-temperature shut off for the burner if the fan isn't blowing. If this one doesn't or the over-temp function isn't working, don't let it get so hot that it burns the house down.

OK, so I undersold my ability to use a multimeter.

I had already mentioned the overheat protection likely triggering the shutoff, and would never do anything to undermine that. I'm just trying to troubleshoot whether the fan motor is dead, or something "upstream" of it is the problem. Any advice is appreciated.

 

[Dana]

Is this the right vintage unit?

The exploded diagrams on p22 and p25 looks like the fan may be connected with push-on connectors. Disconnecting it and verifying that the windings are still continuous with meter on an ohms scale would be a good start. With the meter on VAC scale you should be able to measure the voltage at the wires that were hooked up to the fan.

In the lower left corner of the schematic on p10 it indicates three wires go to the fan, Yellow, Black, and Red. The red wire comes from some component labeled "fan controller" which looks like a make/break switch contact, possibly a relay. In the parts index for the exploded diagram on p19 , index #54 is labeled "fan control switch", but I didn't spot it in the exploded diagrams. Maybe you'll have better luck/eyes than I did.

 

[LarryLeveen]

"Yep, that's him, officer." Two questions:

From videos I have seen, continuity is tested without power to the unit (this heater is easy to unplug from the wall receptacle). Is that correct?

Now, for the voltage at the wires that were hooked up to the fan, it would seem that not only must the heater be plugged in, but that the heater must be both switched on, as well as at a point in its heating up that it would have triggered/energized the fan to start spinning (but before the overheat sensor turns the heater off). Is that also correct, or am I missing something?

Thanks.

 

[Dana]

You've got it- the continuity tests should be done with the unit unplugged, but you can bet the VAC will always be zero until it's both plugged in and turned on.

 

[LarryLeveen]

You've got it- the continuity tests should be done with the unit unplugged, but you can bet the VAC will always be zero until it's both plugged in and turned on.

Just as a follow-up, the blower fan motor was dead. Parts are not available. As a matter of fact, one of the official sources of Monitor parts in North America had never even heard of this model (GF-12)! The other source even checked their "Sanford & Son Pile" for old, used parts. No luck. Other models do not share this type of blower motor. No eBay sellers had a proper replacement motor. One guy in Montana who had a classified ad selling an entire GF-12 unit never returned my calls. This model was from 1981, anyway, so probably dodged a bullet there.

Long story short, ordered a new furnace. Oh well, thanks for your help Dana!

BTW, always get more than one estimate: there was a $1000 difference between the two, with the higher one providing less info, an incomplete spec, and curt/rude communication.

 

[Dana]

If it's not too late, a 3/4 ton ductless mini-split heat pump delivers ~12000 BTU/hr @ +17F outdoors, which a comparable amount of heat as the 14,000 BTU/hr of the GF12, and might come in at a comparable installed price. Operating costs are about the same as natural gas in most markets, CHEAPER than propane in almost every market, and since it's a modulating system it's more comfortable than a wall furnace since it tracks the load, AND it air conditions.

In my area a 3/4 ton brand-name cold-climate mini-split such as a Mitsubishi -FH09NA or Fujitsu -9RLS3H runs $2.5- $3K installed. Those are cold-climate models capable of running down to -13F or colder without crapping out. Depending on your actual location (got a ZIP code?) you may do fine with a less expensive but still pretty-good model that's good down to +5F or so.

 

[LarryLeveen]

If it's not too late, a 3/4 ton ductless mini-split heat pump delivers ~12000 BTU/hr @ +17F outdoors, which a comparable amount of heat as the 14,000 BTU/hr of the GF12, and might come in at a comparable installed price. Operating costs are about the same as natural gas in most markets, CHEAPER than propane in almost every market, and since it's a modulating system it's more comfortable than a wall furnace since it tracks the load, AND it air conditions.

In my area a 3/4 ton brand-name cold-climate mini-split such as a Mitsubishi -FH09NA or Fujitsu -9RLS3H runs $2.5- $3K installed. Those are cold-climate models capable of running down to -13F or colder without crapping out. Depending on your actual location (got a ZIP code?) you may do fine with a less expensive but still pretty-good model that's good down to +5F or so.

Thanks for the tip. We already did order the furnace, and it's $1400 installed, so we are happy about that.