Is this ash leaking from vent pipe on my Oil Burning Furnace

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stejus

Minister of Fire
Jul 29, 2008
1,227
Central MA
I really never paid much attention to the oil burning furnace because I had it maintained yearly. Now that I am wood burning, it's been two years since it last cleaning. Is this ash buildup normal and something that's cleaned when a oil burner tech cleans?
 

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Looks like corrosion in the galvanized steel pipe. Moisture will cause this. I would replace the pipe and make sure everything is clean.
 
Moisture.. it is not coming from the top as the chimney has a rain cap. I am only using the burner for domestic hot water so would this cause moisture build up because of shorter, less hot, burn cycles?
 
Yeah, moisture doesn't have to come from the top. If the unit isn't running much, the pipe stays cool. I would guess these cycles could cause condensation to form which will corrode like you are seeing.
 
stejus said:
I really never paid much attention to the oil burning furnace because I had it maintained yearly. Now that I am wood burning, it's been two years since it last cleaning. Is this ash buildup normal and something that's cleaned when a oil burner tech cleans?

That's not ash. That is flue gas condensation. It makes a mess and will rot out anything it deposits on.

I will make a suggestion. Look at the burner. Something relatively standard like a Beckett burner will have a 'clean cut' oil solenoid valve and the Honeywell fireye controller will have a pre and post purge timer. it will spin the burner with no oil on startup, purging, and trip the oil valve. On shutdown it will close the oil and run the burner fan for a post purge and try to evacuate the remaining flue gas out of the unit. There's also no oil dribbling when the burner is spinning up and slowing down.

If you have a burner with no clean cut solenoid, the flue gas is remaining in the system at cooldown. A new burner may be a relatively low cost upgrade, unless you need a new boiler and burner. If you do your own cleaning, open it up and brush between the sections. It maybe making the same mess inside the boiler. That flue pipe is most likely toast at this point.
 
__dan said:
stejus said:
I really never paid much attention to the oil burning furnace because I had it maintained yearly. Now that I am wood burning, it's been two years since it last cleaning. Is this ash buildup normal and something that's cleaned when a oil burner tech cleans?

That's not ash. That is flue gas condensation. It makes a mess and will rot out anything it deposits on.

I will make a suggestion. Look at the burner. Something relatively standard like a Beckett burner will have a 'clean cut' oil solenoid valve and the Honeywell fireye controller will have a pre and post purge timer. it will spin the burner with no oil on startup, purging, and trip the oil valve. On shutdown it will close the oil and run the burner fan for a post purge and try to evacuate the remaining flue gas out of the unit. There's also no oil dribbling when the burner is spinning up and slowing down.

If you have a burner with no clean cut solenoid, the flue gas is remaining in the system at cooldown. A new burner may be a relatively low cost upgrade, unless you need a new boiler and burner. If you do your own cleaning, open it up and brush between the sections. It maybe making the same mess inside the boiler. That flue pipe is most likely toast at this point.

Now that you say it may be an electrical component (solenoid), it may make sence. We had an electical surge that fried my circulation pump for the forced hot water. The domestic hot water works fine, but the heat triggered by thermostat doesn't because the circ pump was fried. It's a becket burner, about 10 years old. The furnace (boiler) is a Burnham about 20 years. What am I looking for on the burner to point me to the clean cut solenoid?
 
stejus said:
Now that you say it may be an electrical component (solenoid), it may make sence. We had an electical surge that fried my circulation pump for the forced hot water. The domestic hot water works fine, but the heat triggered by thermostat doesn't because the circ pump was fried. It's a becket burner, about 10 years old. The furnace (boiler) is a Burnham about 20 years. What am I looking for on the burner to point me to the clean cut solenoid?

It would be obvious. There's a 10 - 20 second delay on every cycle where the blower motor is spinning with no combustion and when the valve opens, there's the woosh when the firing starts. On the left side, the label on the pump says "cleancut" and the valve sits right on the top of the pump with a wire to the Fireye controller. The Burnham should be a good boiler, cast iron sectional.

That's my first guess, evacuating the flue gas, purging. If the boiler is firing and the through water temp is too low, < 140 deg, that type boiler is not rated for condensing, low temp operation. Boiler operating temp makes a big difference. Return water temp should be > 140 deg. It looks like it may be a tankless coil for DHW, so shorter, more frequent firing cycles. An indirect tank would give you a longer hotter firing cycle. I don't know what the least expensive fix would be. A good boiler guy should look at it.
 
__dan said:
stejus said:
Now that you say it may be an electrical component (solenoid), it may make sence. We had an electical surge that fried my circulation pump for the forced hot water. The domestic hot water works fine, but the heat triggered by thermostat doesn't because the circ pump was fried. It's a becket burner, about 10 years old. The furnace (boiler) is a Burnham about 20 years. What am I looking for on the burner to point me to the clean cut solenoid?

It would be obvious. There's a 10 - 20 second delay on every cycle where the blower motor is spinning with no combustion and when the valve opens, there's the woosh when the firing starts. On the left side, the label on the pump says "cleancut" and the valve sits right on the top of the pump with a wire to the Fireye controller. The Burnham should be a good boiler, cast iron sectional.

That's my first guess, evacuating the flue gas, purging. If the boiler is firing and the through water temp is too low, < 140 deg, that type boiler is not rated for condensing, low temp operation. Boiler operating temp makes a big difference. Return water temp should be > 140 deg. It looks like it may be a tankless coil for DHW, so shorter, more frequent firing cycles. An indirect tank would give you a longer hotter firing cycle. I don't know what the least expensive fix would be. A good boiler guy should look at it.

You may have nailed it with the low water temp. It's a Burnham Cast Iron Boiler. It has a tankless coil and I set the low to 120 with a diff of 10 a few weeks back because we keep burning our hands at the faucet. I figured why use oil to heat the domestic water hotter than what we need it to be. So, you are saying it should be set to min of 150 with a diff of 10 so it never dips below 140.
 
stejus said:
You may have nailed it with the low water temp. It's a Burnham Cast Iron Boiler. It has a tankless coil and I set the low to 120 with a diff of 10 a few weeks back because we keep burning our hands at the faucet. I figured why use oil to heat the domestic water hotter than what we need it to be. So, you are saying it should be set to min of 150 with a diff of 10 so it never dips below 140.

Yes, usually the lowest setting on the aquastat is 160 deg. I'm surprised it would turn down that low. 150 deg may work now that you know what to look for. When you open the boiler for cleaning, it's really surprising how much of a mess the flue gas condensation makes. One look at it and you will run it hot enough to make it stop.

If you're burning, scalding, from hot DHW, you need a mixing, tempering, valve after the tankless coil.
 
__dan said:
stejus said:
You may have nailed it with the low water temp. It's a Burnham Cast Iron Boiler. It has a tankless coil and I set the low to 120 with a diff of 10 a few weeks back because we keep burning our hands at the faucet. I figured why use oil to heat the domestic water hotter than what we need it to be. So, you are saying it should be set to min of 150 with a diff of 10 so it never dips below 140.

Yes, usually the lowest setting on the aquastat is 160 deg. I'm surprised it would turn down that low. 150 deg may work now that you know what to look for. When you open the boiler for cleaning, it's really surprising how much of a mess the flue gas condensation makes. One look at it and you will run it hot enough to make it stop.

If you're burning, scalding, from hot DHW, you need a mixing, tempering, valve after the tankless coil.

The aquastat goes down to 120. I just set it to 150 for the low. We don't cycle the forced hot water much so it's basically running of the low year round. We do have a mixer valve and it is wide open (to add more cold water). I'll clean and then take a look in a few weeks. Thanks for suggestions!
 
Do you not have a T for the moisture to drip to??

I just did a roof vent for my boiler, before it goes into the boiler there is a T. At the bottom of the T we put a hose that goes to my drain line. I didn't figure it would make much water but it filled a small pail (maybe 1 gallon) in under a month.
 
You're likely to get condensation where the flue pipe meets the thimble because the thermal mass takes a while to heat up and with little useage and low temperatures it probably never gets up to temperature.
 
NATE379 - my setup is what you see in the first picture. The vent pipe goes into the thimble. On the other side of the thimble is exterior clay tiled chimney.

Fred61
- I suspect this as well. I found this text in a Burnham Boiler C3 - C4 Oil Fired Boiler. I would suspect I am not the only one with this issue. I have basically taken my Oil Fired Furnace and reduced it to a domestic hot water heater (short infrequent heat cycles). I really don't know when it started and it may be because i set the LOW temp way too low. I had it at 120. It put it back to 150 and maybe this will help burn off some of that condensation because it will run a little longer and more frequent.

The combination of a large uninsulated
chimney, reduced firing rate, reduced firing time,
lower stack temperature and less dilution air can,
in some cases, contribute to the condensing of
small amounts of water vapor in the chimney.
 
The thimble going through the concrete wall will actually be a bigger heat sink than the upright flue tiles because it is usually packed tight with mortar giving it a perfect connection with the concrete foundation wall. Clay flue tiles are basically floating in the brick enclosure of your chimney.
 
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