Gas and Oil Home Heating Furnaces - Problems with an old oil furnace.

I bought a 1967 Bostonian Mobile Home last year. I live near Carlisle PA. The temperature has been averaging in the high 20's to low 30's at night. I have an above ground tank and am running straight fuel oil with plenty of anti-gelling agent.

Information I took off various places on my furnace:

Miller -- MA100
Wayne MP98 (burner I think) -- M-SRH
Lear Siegler Inc. - MOC 80-1

Motor, and fuel pump were replaced in late 2004.
The information I have from 2004 has a safety timing of 45, a pump pressure of 100, and the OHMS at 500.
Thermostat is a dial type with a liquid mercury trip...set to kick on when it drops 3 degrees below what it's set.

The furnace has been failing to kick back on when the thermostat goes below the setting. It'll fire right up when I press the reset button. Until recently it would run fine for a while, then have the same problem. Now the burner activates for about a minute or two, then will shut down. About 45 seconds later the fan will kick on. From what I can understand this is a normal start up cycle for a Miller. Unfortunately it no longer goes beyond this cycle. When the fan is running I get it to kick off and back on by adjusting the thermostat.

I have had three different repairmen in over the last month, with varying degees of success.

1st repairman couldn't find anything wrong...thankfully didn't charge me.

2nd repairman replaced one nozzle and electrode, and adjusted the burner position. Told me the furnace was built in 1965, and was on it's last legs. Of course he offered to install a replacement. Charged me $108. The unit ran ok for a couple of days.

3rd repairman (who was apparently trained on the old Miller's), replaced both nozzles and the electrode. (Showed me the two nozzles he pulled out before he went to his truck for replacements...definately 2 different kinds). He adjusted the oil pressure from 130 to 100. He also cleaned the blower assembly and adjusted the motor bracket and fan. He told me the original furnace had been replaced with one from the 70's. Charged me $207. The unit ran great for a bit over a week.

It has now gotten worse (see above). I know very little about furnaces, so DIY is probably out. However, I feel like at least two of the repairmen were incompetent if not down right fradulent. I am willing to call a repairman again, but I'd like some idea of 1) what I have, and 2) what is likely to be the problem. I wasn't happy with the attitude of the 2nd one, so even if he's right, I'll not use him again. Given the above information does the 3rd repaiman seem trustworthy?

Thanks for any help you can give me,

Pam

I hate to be the bearer of bad news but the guy who said the furnace is on it's last leg is likely right. Any Miller, 30 years old, has lived two normal life expectancies. I would be amazed if the heat exchanger were not cracked. This furnace held up fairly well with the original burner but the higher temperatures of a flame retention burner was real tough on them. The number of MOC's on which I've worked in the past 20 years would fill a good sized warehouse. Something to try, just for testing purposes, is to turn the thermostat up all the way. If it continues to run as normal, the thermostat is a good candidate for the cause of your trouble.

Information I took off various places on my furnace

You deserve help just because you are making a solid effort yourself.

> Motor, and fuel pump were replaced in late 2004.

Okay, I hope that it was verified at the time that your heat exchanger is in great shape and this was a worthwhile investment.




> 1st repairman couldn't find anything wrong...thankfully didn't charge me.

Honest.

> 2nd repairman replaced one nozzle and electrode, and adjusted the burner
> position. Told me the furnace was built in 1965, and was on its last legs.

Truthfully, I'd rather install a new one than work on an old one.
Sometimes you just know that it will cost more to rebuild an old one than to replace it.


> 3rd repairman (who was apparently trained on the old Millers),
> replaced both nozzles and the electrode. ...
> He adjusted the oil pressure from 130 to 100.
> He also cleaned the blower assembly and adjusted the motor bracket
> and fan. He told me the original furnace had been replaced with one
> from the 1970s. Charged me $207.
> The unit ran great for a bit over a week.

Okay.

> However, I feel like at least two of the repairmen were incompetent
> if not down right fradulent.

I'd be more forgiving.
They probably figured that you didn't want to spend a lot to repair it when a new one would serve you better.


> I wasn't happy with the attitude of the 2nd one, so even if he's right,
> I'll not use him again.

Fair enough. I know that type that just don't seem to have the time for what they consider junk.



> Given the above information does the 3rd repairman seem trustworthy?
Can't say. He was throrough. I'd call him again.

Perhaps Grady (who I gather recognizes your model) or someone else can help you here.

I'm thinking that your unit has a cadmium flame sensor (usually two yellow wires stuck together coming out of the burner area).

You didn't mention it.

But a failed or sooted sensor would produce symptoms like you describe depending on the control board (run a short time and pop the button).


Otherwise, it must have a sensor on the exhaust flue that isn't reporting hot flue gases. So the button pops.

I didn't catch the exact thing you did with the tstat, but I think you mean that the tstat works, but only until the button pops.


My guess from too far away: bad sensor.

The burner running for a minute or two, shutting down, & the fan coming on, is typical MOC. Miller put in a low temperature secondary limit to allow the heat exchanger to come up to operating temperature more slowly. It would have been better to reposition the fan/limit but it was cheap, quick, & easy to put in a lower temperature secondary limit. If you see an MOC that doesn't do this, somebody has changed the limit to a higher temperature one.
Sometimes the MOC will cycle a couple of times on the secondary limit before the burner & fan run together. MOC's tend to crack at the upper corners of the combustion chamber opening. To see it you have to pull the burner & front panel.

The burner running for a minute or two, shutting down, & the fan coming on, is typical MOC.
Lovely. Thanks.
I'd say replace it if the lady hadn't just invested so much money in new parts.


> MOC's tend to crack at the upper corners of the combustion chamber opening.
> To see it you have to pull the burner & front panel.

So it might not have been inspected and even if it was, it could have cracked the next time it fired?


Anyway, about the button popping...

Flame sensor, flue temperature, or what?



Pam,

If you watch the fire, which happens?
(1) button pops and fire goes out or
(2) fires goes out than button pops a little later.

Thanks for the answers so far.

To answer some questions:

Garey: I tried setting the thermostat clear up, and the same thing that it usually does happened.

Bolide:
"Okay, I hope that it was verified at the time that your heat exchanger is in great shape and this was a worthwhile investment.

Now the burner activates for about a minute or two, then will shut down.
About 45 seconds later the fan will kick on.
From what I can understand this is a normal start up cycle for a Miller.

Who said this??"
The Information on what was done in 2004 is from a maintaince booklet from the previous owners oil company.

As far as the start up cycle...I beleive it was the 3rd repairman that mentioned that.

However, I feel like at least two of the repairmen were incompetent
if not down right fradulent.

I'd be more forgiving.
They probably figured that you didn't want to spend a lot to repair it when a new one would serve you better.

I wasn't happy with the attitude of the 2nd one, so even if he's right,
I'll not use him again.

Fair enough. I know that type that just don't seem to have the time for what they consider junk.

In a way, he did you a favor.

My big problem with the second repairman was the fact that he obviously put in an incorrect nozzle. The two the 3rd guy pulled out were very obviously two different nozzles. I had kept the one the second guy pulled, and he did replace it with a wrong one. I also suspect he was the one that raised the pump pressure.

The button pops then the fire immediately goes out.

If I have to, I'll replace the furnace, but I'd like to exaust all possibilities first.

My big problem with the second repairman was the fact that he obviously put in an incorrect nozzle.

It's not obvious to me. There is some leeway here, flow, cone angle, and pattern.
They might have been different manufacturers which means that the equivalent can be a bit different.

But I see your point.
And if repairman #3 said it was wrong, I would say that is probably true.


> I also suspect he was the one that raised the pump pressure.
Either dumb or experimenting.
I would have to hear from him he was thinking.

bolide,

I'll admit I'm probably over-reacting a bit on the 2nd repairman.

Pam

If you watch the fire, which happens?
(1) button pops and fire goes out or
(2) fires goes out than button pops a little later.

bolide,

The button pops and the fire immediately goes out.

Pam

The button pops and the fire immediately goes out.Sound like a sensor problem.

The other way around would be a different problem.

Thanks for the help. It gives me some idea of what might be going on when I call the repairmen.

Pam

I agree that the cad cell is likely the problem.

Thank you both. I'll let you know how everything turns out.

Pam

I agree that the cad cell is a possible cause.The other thing to think about is an incorrect flame can cause the same problem.If there is any moisture in the oil it can cause the cad cell to fail the unit because water does not burn.I have not heard mention of the fuel filter being changed.Was the tank completly full all summer?If not,then you could have some moisture in the tank.Just some food for thought.Good luck!!

it can cause the cad cell to fail the unit because water does not burn.
Pam did say that the button pops first, then the flame goes out - not the other way around.

Pam did say that the button pops first, then the flame goes out - not the other way around.

If there is water in the system the flame could studder enough to trip the flame safty.I did not know if she was actually sitting in front of the furnace and watching it run all the time.I read the post just like you did.I was trying to give some suggestions of possible situations that may occur.