Monitor 41 issue

[cadman44]

Looking from the front of the unit, there are two thermostats on the top right and one located more middle left.

The left one is the fan thermostat. The parts diagram I am looking at only has a leader to one of the adjacent ones on the top right and calls it the overheat thermostat. Which one should I jumper?

[HayZee518]

the top one that's the fan control. the other two are connected in series and are the overheat stats.

[cadman44]

Ok, so I just bypassed the fan switch (the single one not the one in series on the right). I plugged the unit back in and the fan started right away. I turned on the unit and am still seeing the same problem. It goes through the start up routine (about 4-5 minutes), the heater turns on, and then after a couple of minutes, it shuts down with all eight bars blinking. Does that tell you anything?

[cadman44]

Also, what is this e-14 error that I have seen throughout the forum? How do I tell if that is the error that I am getting?

[HayZee518]

sorry, E-14 is indicated on the 2400 vented heater. the older units used those orange burner lights according to burner status. eight flashing lights mean overheat or no flame and flame rod lockout in the main board. to check the flamerod circuitry get a diode and a 100K resistor. connect the diode and resistor in series. use some hookup wire and solder to the diode lead and resistor lead. when the heater is on with a flame, disconnect the flamerod wires and substitute the resistor/diode assembly in the jacks. if the polarity is correct the heater will shift into high heat and keep running. if it shuts down and goes into lockout, reverse the resistor/diode assembly and try again. now it should stay running. if you pull out the thermistor connector, the heater defaults to 42 degrees and stays lit. no need to set the setpoint to 90 degrees.

[cadman44]

Ok, I will hit Radio Shack tomorrow after work.

I am good up until your last two sentences:

if you pull out the thermistor connector, the heater defaults to 42 degrees and stays lit. no need to set the setpoint to 90 degrees.

What is the thermistor connector?

[dfitz3390]

no it closes thats why they call it normally open

[HayZee518]

on the back of all monitors including the propane ones, you'll see a white paired zip-lead that either goes directly into the heater or into a "molex" plug that can be unplugged. this device is what senses the temperature of the room and changes its resistance according to temperature. this changing resistance is sensed by the heater to start-up, maintain a steady temperature and/or shut down the heater as the room temperature reaches the set point setting. the wire is split in two inside the heater and plugs into the motherboard computer. removing the wires will default the heater to 42 degrees and the heater will not shut down, unless the unit has gone into lockout.

[cadman44]

Oh, that makes sense now. If I thought about it a little more I would have figured it out. I will try to check this tonight.

[adnadeau]

Flame Sensor check

Another way to check flame sensor operation is to connect your VOM (3VDC scale) between test points EP and TP6 on the PWB. With no flame you should see 0VDC. As the unit fires up, the voltage should climb to at least 1.2VDC. Point EP(0V) is on the upper right corner of the board and is the common point for all the DC circuits.

Correction: In the Monitor 441 it's TP6; in the 41 it's TP7.

[cadman44]

Ok, I tested TP7 to EP. With no flame I had 0.03-0.04 VDC. With flame it climbed as far as 0.98 VDC but no higher. You mentioned that it should go to at least 1.2 VDC. What does this tell us? Is the flame rod bad?

Should I go through the exercise of getting a resistor and diode or does this tell us what we need to know?

[HayZee518]

it wouldn't hurt to buy the resistor/diode combination, make it up and use it to troubleshoot your heater. the flamerod is nothing special, other than a piece of metal that doesn't melt in a flame, is insulated by a porcelain tube. in the presence of a flame it changes its electrical characteristics. The air which surrounds it, in a flame, is ionized, that means the air conducts electrons. it is a "PLASMA" effect. normally it has an AC potential on it but changes to DC in a flame. there's a whole website that explains it.

[adnadeau]

I agree with Hayzee. Try the resistor-diode bypass just to confirm that the flame detector is not working. The rest of the circuit may be okay; the bypass will show that.
See if you can measure the 120VAC secondary of the pwr xfmr that feeds the flame detector circuit. One leg of that feeds out to the case of the 41 through the green "ground" wire that is under a screw head near the PWB. Also, if you haven't already done this, remove the 2 screws that hold the flame rod, remove it and check for corrosion etc. There are many other posts here with details on how to do this.

[adnadeau]

441 Flame Detector Schematic

Here's the schematic of the 441 flame detector circuit.

[cadman44]

I have previously taken out the flame rod and checked for corrosion/carbon buildup. It seems ok. I will not be able to get back onto this until Saturday. I will do the bypass test this weekend and post my results.