Monitor 441 - burner won't stay lit...intake pressure switch?

[dfitz3390]

Hayzee my manual says the pump is pulsed DC i had a problem with one unit once that had a fuel delivery problem the small rubber tip on the needle valve came off the the needle and was restricting fuel flow to the constant level valve itself. may not be your problem but might pay to throughly look. does the pump start to change sound around the time it shuts off ?

[HayZee518]

ok, -ashadowalker- I stand to be corrected then. dfitz pointed out that the pump is DC. the pump has a hollow core with like a check valve that moves. its pretty much like an old water lift pump found on rural farms, but multi-miniature in size. there's a return spring inside and a core and coil. when it energizes the core is sucked up into the coil, closing the check valve "flapper" - when it relaxes the spring drives the core back down and opens the flapper. when it reaches bottom, the core is sucked back up, then back down again. the core is pulsed so the flapper opens and closes many times a second and imparts a pumping action for the fuel. a normal sounding pump makes almost an imperceptable thumping noise as it pumps. when there is no fuel the thumping sound gets louder and louder and the flamerod takes over and shuts down the heater.
The kerosene although imflammable is also an oil of sorts and lubricates the pump innards.

[adnadeau]

Solenoid Damper O-ring

The damper solenoid, although 120VAC is printed on top, operates on DC in the 441. I tried AC on mine and it didn't move. If you hear it "clunk" when it pulls in in normal heater operation, then it's working, regardless of its resistance. The O-ring is located on the solenoid piston shaft and acts as a bumper to reduce the pull-in noise. It is a common black rubber type, 7mm ID, 11mm OD, 2mm thick. Look in the solenoid compartment in the blower for pieces of the old one if it's not still on the solenoid shaft.

[ashadowalker]

Hi guys,

Time for an update. After my last post I lubed the bearings on the combustion blower and reassembled it. I also checked the air pipe between the blower and the burn chamber (which was clean and clear). When I started the unit up again, it still wouldn’t proceed past the pre-combustion-2 stage. As a final check of the air supply system I forced air into the intake with a shop-vac while running the start-up sequence. The pressure obviously wasn’t a good match because I never got any flame. However, when I next tried to start the unit….lo and behold! It worked! WTF????? It functioned all night, turning itself on and off like it’s supposed to.

So, proceeding on the premise that the burn chamber wasn’t getting enough air, I opened it up the next day. I brushed the walls (for the second time) with a wire brush and poked a Glover’s needle through all the air holes in the burn pot. I sanded the flamerod shiny. I vacuumed the pot and put it back together. After this the unit once again wouldn’t proceed past pre-combustion-2. I tried the forced air trick again but there was no change. The following day I built the flamerod by-pass shown on page 51 of the service manual and used it. I’m so glad I did! With the bypass installed the heater operates just as it’s supposed to. This eliminates the board, the pressure switch, the solenoid pump and it’s controller as possible causes of the shut-down. I ran the unit for an hour and everything works as it should. So, the flamerod is causing the shut-down. It could be a short in the wire from the board to the flamerod; It could be a faulty flamerod; Or the flamerod could be doing its job and I still haven’t made progress towards diagnosing the problem.



More recent update: I’ve replaced the flamerod (there was an intermittent short in the old one). The unit now works most of the time but still has occasional trouble with a cold start to a low setting. There are surges of yellow flame under these conditions and sometimes the flamerod triggers a lockout. I can use the flamerod bypass to proceed past this stage. At higher settings the yellow flame disappears and when I return the flamerod to the circuit it doesn’t shut anything down, even when the unit drops to the lowest setting. I suspect there is insufficient air in the burn chamber to satisfy the flamerod when the blower is on low and the solenoid damper is closed. I have a few thoughts as to why the warmup makes a difference but no way to know if any of them are correct.

I don’t have a manometer so I can’t test the air pressure. I’ve replaced the bearings in the combustion blower (at 15 years old they needed replacing anyways). I’ve checked the intake and exhaust lines but they were clear of obstructions. The combustion blower motor has the correct resistance, so there are no shorts in the windings. However, the resistor that plugs into G on the main printed wiring board, which is supposed to have a resistance of 91, only has 88 ohms. This resistor (part # 6338) is in the same circuit as IC9, which actuates and empowers the low speed setting for the combustion blower motor. Maybe this little difference is enough? I need to track down a replacement for this resistor. Can anyone tell me anything about it? I haven't found any specs for it in the service manual. In the meantime I’m going to be playing with preventing the solenoid damper from closing fully so a little more air makes it to the burn chamber. Hopefully this will tell me if I’m on the right track.

[adnadeau]

resistor

The combustion resistor is a 20 Watt, 91 Ohm, 5% (J) tolerance power resistor. The tolerance of 5% times 91 Ohms gives a range 91 +/- 4.55 Ohms, so 88 Ohms is fine.

[adnadeau]

How did you "check the pipe between the blower & the combustion chamber"? I ended up using a shop vac to vacuum out the pipe on the combustion chamber side and also vacuum out the hose going to the through-the-wall fitting. Things worked fine after that. I had also replaced the solenoid damper O-ring, so that let a little more air in.

[ashadowalker]

11/17/2011 So, today’s heater update. Since yesterday I’ve removed the restricting ring from the exhaust pipe, moved the solenoid damper, and installed an adjustment screw to control how far the solenoid damper closes. Though I installed an adjusting screw I haven’t had to use it, yet. I loosened the two screws that hold the solenoid to the blower housing and adjusted it as far up as they would go. This was only about 1/8 of an inch but seems to have been sufficient to my needs. The heater has been cold starting to a low flame with no difficulty since last night. Also, the surging yellow flame is no longer present at low settings. We’ll see how long it continues to behave, this time. Here is a short list of the repairs that have made a difference in the performance of the heater: fuel pressure from external tank (filled tank), new flamerod, air adjustments (new bearings in combustion blower, remove exhaust restrictions, adjust damper solenoid).

adnadeau, thanks for the data on the resistor. I checked the pipe between the blower and burn chamber by removing it and both rubber elbows. Upon inspection there were no obstructions, just a little dust. Applying the shop-vac to the exhaust line sounds like a good idea. I ran a wire through the length of it this time but at 13 feet and 2 elbows it was a hassle. Especially since there were no obstructions. Next year I’ll be using the shop-vac first.

[HayZee518]

how is it your exhaust and air inlet extension is 13 feet? I never seen one greater than four feet!

[ashadowalker]

According to the service manual there are 4 extension kits available. Page 17 of the service manual illustrates the max lengths and bends allowable using these kits. We live in a house built before 1900. The 441 heater sits where the kitchen stove used to, back to back with the big stone fireplace (they used to share the chimney), in the middle of a room. When the Monitor techs originally installed the heater they ran the exhaust and intake pipes down through the floor into the crawl space and then out through the foundation at the nearest point. Whenever a service tech comes out they try to talk the homeowner into moving the heater against an outside wall but it's stayed where it is for 15 years. In fact, the length of the exhaust pipe had crossed my mind as a possible contributing factor to our air supply problems however, there would have been problems since installation. We don't get enough snow for the exhaust to be in danger of being blocked and having the heater in a central location is good for heat distribution. I'm not sure what else to say...yes, it's at the outer limit of what's recommended but it hasn't been a problem for 15 years. Yay Monitor!

[dfitz3390]

it may be time to check the differential pressure, i know that adjusting the damper even slightly can make a big difference on low fire and if the diff. is too great it can lead to excessive heat and warping. you can purchase something for about 65 bucks if you have the use . It seems like the only thing that you didn't mention. I assume you have cleaned the heat exchanger and checked for restrictions. good luck

low fire damper closed 2.5 - 3.0 mm/H2o
hi fire damper open 6.5 - 7.4 "