# Monitor Heater flame rod bypass test?



## Alan (Apr 12, 2006)

I'm having troubles with a monitor heater and a little research has led me to the fact that testing the flamerod is the easiest way to figure out the problem.

Apparently there is a small circuit that can be made to trick the heater into thinking the flamerod detects a flame so that way you can determine whether bad flamerod or bad PCB.

I dont have a radio shack near me anymore and im a little confused about the diode that is supposedly used.

If anyone knows anything about these can you link me to a proper diode so that I can be sure to order the right one?

Service manual is very blurry and difficult to read.

Thanks in advance.


----------



## yuri (Nov 29, 2008)

I had one 30 yrs ago to test Lennox G8E furnaces but don't know who made it.

Flame rods never go bad unless the porcelain which holds it is very black or cracked.

Take it out and clean the rod with clean steel wool or #800 emory paper. I would not try the diode biz or waste time sourcing it. Have not heard of it in 30 yrs and nobody I know uses it anymore.

Post a pic of the burners and flame rod. Does it use a spark for ignition or glowing hot surface ignitor?


----------



## Alan (Apr 12, 2006)

I already took the rod out and it looked pretty clean. 

Not sure about the ignition but id have to do more research to be certain.
First time the new tenants ran it, they had the valve to the tank off. I rectified that and told them the air should purge after it tries to run for a bit. It came on, the fan turned on like normal and then we shut it down because it was a hot day and not needed.
They called again saying it was still having issues so they took it apart and cleaned it. :vs_mad:
So I went back, disconnected the fuel line and purged the air. Checked the filter at the unit and visual inspection of everything to make sure nothing looked severely out of whack.
The last time I ran it, the circ fan didnt come on either, so I was thinking that the tenant switched some of the wires to sensors on top of the cabinet around. Top of cabinet got really hot.
They swear they didnt but i cant think of another reason the circ fan wouldnt come on unless pcb is going bad.


----------



## user_12345a (Nov 23, 2014)

the flame signal can be checked with a meter that does dc microamps.

bad grounding and many other things may cause a low flame current, don't blame the rod.


----------



## yuri (Nov 29, 2008)

Is this a oil furnace or Propane?


----------



## Alan (Apr 12, 2006)

user_12345a said:


> the flame signal can be checked with a meter that does dc microamps.
> 
> bad grounding and many other things may cause a low flame current, don't blame the rod.


I have a craftsman meter that im pretty sure does dc microamps. Can you describe where to test and how much current Im looking for?

The heater runs on Kerosene.


----------



## user_12345a (Nov 23, 2014)

If your heater uses flame rectification to prove ignition set it to dc microamps and put the leads in series with the flame sensor.

there are a few articles on this.

a kerosene heater is more likely to have an oil style burner than anything else -> those don't detect flame the same way. flame rectification with a metal rod is used on gas/propane.


----------



## yuri (Nov 29, 2008)

Is it a room heater?

I have never worked on one, not sure if anyone else here does.

Does your unit look like this?


----------



## beenthere (Oct 11, 2008)

If the heater got real hot. Good chance the burner **** off on high limit and you just have to determine why the blower isn't working.


----------



## BruceLem (Jan 25, 2020)

Here's a picture of the Monitor 422 Flame Rod bypass circuit.

I tried it and it worked perfectly for me and allowed me to get past the 3:40 minute mark to full heater output.

The text says: 
"FLAME ROD BYPASS CIRCUIT

For testing purposes, a flame detector rod bypass circuit can ba made up consisting of 2 insulated alligator clips. 2 8" pieces of insulated copper wire, 1-1/4 watt 400 volt diode, and 1-1/4 watt 100k OHM resistor. These components are to be soldered together in sequence as shown in diagram below (note component sequence and polarity).

Once the bypass circuit is made the unit is tuned on. Immediately after the preheat prepurge cycle: when mode light comes on. The O and N pins are disconnected off the PCB and replaced with the bypass circuit The unit should then continue functioning as though it had a good flame inside the burn chamber and service tests such as fuel flow can be checked.

(Note: WARNING after all tests are completed, replace original flame rod wires as it is a vital safety feature.)"

Attached image:


----------

