Monitor 441 not cycling properly

[AndyF]

Hi,

I purchased a used Monitor 441 and am planning to use it in a small greenhouse. Several weeks ago when I first tried to use it, it would start fine and run through at least 1-2 heating cycles and then stop running (I'd come back several hours later and find the burner indicators flashing). I've cleaned the burn pot, which didn't have much soot at all, checked the flame sensor, and reassembled the heater. When I tried it today, it started fine, ran through 2 cycles with no problems, I came back 2 hours later to flashing burner indicators and when I tried to restart it, it tried to cycle, but I didn't get a flame.

Any ideas on what to check next or why it will start OK, run a cycle or two or three and then not be able to achieve ignition?

[HayZee518]

monitor

check for an obstruction at the air inlet. the fuel level in the outside tank should be around 18 inches higher than the fuel inlet pipe on the heater. the fuel flow is gravity feed all the way to the oil sump and oil pump. reason for the height is to provide adequate pressure to fill the oil sump when the heater kicks into high.
when the fuel goes low it locks out the pump and stops the heater. that's why you get the flashing lights. try unplugging the heater then plug it back in. this resets the internal computer.

[Bryand]

Chances are very good the oil line going into the burner is stopped up but be aware when you take it off the line could break loose from the burner pot. You should be able to run a 1/8" drill bit at least 4" down inside the oil inlet to the burner. If that is not it when you find it flashing start it back up and see if you hear the fuel pump making a pretty loud thumping sound when it starts pumping fuel. That will be the indicator that it either has air in the oil line or starving for fuel for some reason.

[AndyF]

Thanks for the suggestions so far.

The Monitor is getting fuel from a full 275 gallon tank with new Kerosene and a new filter on the tank. When I crack the compression fitting connecting the fuel line to the heater I get a steady flow of kerosene.

I do not hear any thumping from the fuel pump, but do feel a steady vibration when I put a finger on the pump when it is trying to run.

The exhaust/air inlet on the outside of the greenhouse is unobstructed and the flexible hose to the fan is unobstructed, the fan seems to be working fine. Are there any other areas on the air side which should be checked.

Bryand, why are you suggesting a stopped up fuel line? The heater seems to run fine for 1-2 cycles with greater than 10 minutes burner on time for both cycles and at some point after that will not fire.

[Bryand]

Thanks for the suggestions so far.

The Monitor is getting fuel from a full 275 gallon tank with new Kerosene and a new filter on the tank. When I crack the compression fitting connecting the fuel line to the heater I get a steady flow of kerosene.

I do not hear any thumping from the fuel pump, but do feel a steady vibration when I put a finger on the pump when it is trying to run.

The exhaust/air inlet on the outside of the greenhouse is unobstructed and the flexible hose to the fan is unobstructed, the fan seems to be working fine. Are there any other areas on the air side which should be checked.

Bryand, why are you suggesting a stopped up fuel line? The heater seems to run fine for 1-2 cycles with greater than 10 minutes burner on time for both cycles and at some point after that will not fire.

Looks like you are now down to the fuel line. Here is the reasoning. The line may not be entirely clogged with carbon but enough that it is not allowing the pump to pump all the fuel needed to run the heater on high or run for long periods of time. I know you are going to be told not to use a drill but sometimes you have to. If you use a drill and a 1/8 inch bit you can tell when you get thru the carbon and to the ignitor rail. The sound is different and also you will feel a give in the drilling before it gets to the ignitor rail. As long as your burner sensor does not have carbon on it now and is not touching the burner ring then I would be almost 99% sure the line is clogged. Once you have done it long enough you can actually hold the oil line and feel the pressure from the pump and tell if it is clogged. Also another sign is to look at the burner ring when it is running on high. The burner ring should be glowing red. If the line is stopped up it will not be that red and may have areas of black on the ring where the heater is not getting hot enough.

[HayZee518]

heater

try this, make up a jumper with wire and two alligator clips. clip the wire across the terminals of the air switch and try the heater. if it runs and doesn't stop then your air switch is faulty.
another thing to consider is, if you unplug the thermistor, the heater will default to 42 degrees and will stay running on high.
with the heater running on high, you can pretty much isolate the problem to either the sump tank or the fuel pump. less than adequate fuel in the sump will cause the pump to fail and the heater will shut down and lockout.

[HayZee518]

flamerod test

for your "toolbox" go to radio shack and get a 1N4004 diode and a 100K resistor [brown, black, yellow} bands and connect the diode and resistor in series. now splice in two lengths of wire with two alligator clips. when your heater is firing up connect the resistor/diode across ground and the flamerod wire on the mother board. if your polarity is correct the heater should stay running. if it shuts down, reverse the connection and try again. if it shuts down then your problem is in the flame sense circuit of the mother board OR the flame rod itself.
the flamerod normally sits in between the space between the pot and the burner ring. no flame, there is no ionized air. with a flame there is ionized air in that space which conducts current. no flame there is 120 volts AC between ground and the rod. with a flame there is 120 volts DC going to the mother board flame sense circuit.
that's the reason you use a diode and resistor to test the circuit. the resistor limits the current.

[Bryand]

Not trying to step on anyone's toes just want everyone to be safe I have seen some bad things happen over the past 25 years by trial and error. If your heater is quitting then it is apparent that you have a mechanical or safety issue that is causing your heater to shut down. When you bypass something you are forcing the heater to do something it has been told not to do. You can force this heater to do a lot of things. However once I saw a heat exchanger blow apart and I quit forcing them to do anything. A exhaust pipe was almost completly covered with snow and couldn't push any air out but was able to bring some in. I saw my father in law who had worked on them from the day they came out force one to light by crossing over the j plug on the circut board without checking the pipe and the ignition blew the heat exchanger apart so be careful if you force it to work.

[HayZee518]

heater

I was just going by the premise that the OP said the inlet and outlet pipes and the flex hose was clear.
I AM aware of the explosive nature of the beast.

[AndyF]

try this, make up a jumper with wire and two alligator clips. clip the wire across the terminals of the air switch and try the heater. if it runs and doesn't stop then your air switch is faulty.

Hi Everyone,

This is Erik (Andy's son) posting.

I've been tasked with taking a look at this furnace with a second set of eyes. I'm picking up on the troubleshooting where my Dad left off.

I've made up a jumper wire to remove the air switch, I restarted the furnace and it seems to be firing properly. Is see on the main-board that the switch is called out as an (air pressure switch) and I see what looks like a barbed fitting on the front of the switch, there is nothing connected and I do not see any loose lines. Should there be an air feed/return line to the front of the switch?

For now I'll leave it running with the air switch removed and see if there is any difference in cycling. If there's not I'll move on to the next step in the electrical troubleshooting.

-Erik

[HayZee518]

air proving switch

there should be a rubber hose on one barbed nipple the other one is open to atmosphere. its function is to detect air flow from the blower to the combustion pot. if there are NO hoses connected to either nipple then there lies your problem. that switch must be closed with air flow in order for the next chain of events to happen.

[AndyF]

Hi Everyone,

This is Erik again, just wanted to update the thread. I finally did the diode-resister jumper to take the flame rod out of the system. The heater now seems to cycle fine and has been running for a few hours with no issues where previously I had hardly been able to keep it running for 5 minutes.

The flame pattern looks okay to my eye but I'm no expert. Is there a way I can test the flame rod once I have it removed to verify that it's bad and the issue is not with the flame itself?

-Erik

[adnadeau]

The flame rod is just that: a rod. The resistance from the tip of the flame rod to the "O" connector pin should be around zero with the rod & it's wire removed. If you haven't removed it yet from the chamber, remove the "O" connector from the PCB. Measure the resistance from the connector on the wire to the chamber surface or a screw head; it should be at infinity. If there's any resistance showing, there's probably a crud buildup inside the pot where the rod sits.

[HayZee518]

flamerod resistance

as adnadeau said, the flamerod is just a rod. a piece of metal that doesn't melt when it is within a flame.
however it has an AC voltage on it when it is not conducting - 120 volts AC to ground.
Within a flame, its characteristics change. the space between the burner head and the chamber wall becomes ionized, that is to say it conducts electricity BUT at a DC voltage.
That is the reason the test setup uses a diode and resistor.
It cannot be user serviced.

[AndyF]

I'm ready to throw in the towel now on this heater. We received the new flame sensor. Before installing the sensor I opened up the combustion chamber to clean it because we had seen a fair amount of yellow flames through the window when we were running the heater with the resistor and diode rather than the flame sensor.

There was a fair amount of carbon on top of the dome over the burner which I vacuumed off. When I opened up the burner pot I found a wet coke like carbon build up on portions of the burner mat and by the end of the tube which delivers fuel to the burner mat. I cleaned everything up, reamed out the fuel tube with a piece of wire, blew out the fuel line from the fuel pump to the combustion chamber, put everything back together, tried it out and it didn't work right.

It started to go through the start up cycle, got to the point where the burner lights, I observed some blue flame in the around the edge of the combustion chamber and then the pump seemed to stop pumping and the fire went out. I turned off the unit, unplugged it and restarted it and it started up nicely and ran for awhile. I came back several hours later and it had stopped running. I started it again and it started to fire and then shut down. I tried it again the next morning and could not get it to fire and the pump seemed to work for only a minute or so.

So, maybe there is a problem with the pump? or what? I'm getting tired of hanging parts on this heater and not getting any closer to truly fixing it.

Is there someone within 1-2 hours of either Rochester or Syracuse NY who is good at troubleshooting and fixing these heaters? I'd like to have someone who knows their stuff figure out what is going on here and either get it fixed or scrap it.

I'm planning to use the heater in a small greenhouse so it is important that it be reliable. If it fails at night I can lose several thousand dollars worth of plants before morning comes and I realize it's not working.