Corroded flue vent

PB

I have a two year old Buderus boiler on a GHW conversion that has pinholes in the galvanized flue pipe. This seems premature to me. Inspection in the firebox shows no visible corrosion inside on the boiler sections. Why would this be happening so soon?

I will be replacing pipe before I turn on the unit, but I would like to stop the problem from recurring.

THX

Patrick

Mark Hunt

Could be


a couple of things.

Can you be a little more specific? Like which Buderus boiler it is and what type of system is it connected to?

Also, what type of chimney do you have?

Mark H

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

John@Reliable_4

Could it be?

What gauge pipe is it? Sometimes I find duct pipe vs flue piping. Also is it a cold start boiler, if so best to service at end of heating season to remove combustion by-products that can/will eat pipe away.

PB

More details as requested

The boiler is a Buderus natural gas fired unit - G224-45, with a Tekmar 260 outdoor reset. The house is a converted gravity hot water system with two large supply and return mains. System is circulated using a small B&G (I think wet rotor) circulator (It is not the big B&G series 100). Radiation is primarily large cast iron. Several of the rads have Danfoss thermostatic valves installed. New near boiler piping that was installed with boiler is copper. It includes a large expansion tank, isolation valves and a sprirovent. There are no mixing valves or bypasses on the near boiler piping.

The flue is an approximately 8" diameter galvanized sheet metal pipe. It rises up from the boiler about six inches, then takes a 45 degree angle for about 2 feet to clear some of the near boiler piping, and then it angles horizontally into the chimney. The Chimney is a masonry chimney with a stainless steel liner. There is a drain-pipe that drains liquid (condensate or water)? from the base of the liner into a floor drain. The boiler shares the liner with a gas fired water heater. I plan on replacing the hot water heater with a hot water maker when the hot water heater finally dies.

Hope this is enough info.

PB

Reply

By cold start - I presume you mean no pilot. It has Honeywell controls with electronic ignition with a Honeywell flue damper.

Also - the pipe appears to me to be flue pipe and not lighter gauge duct pipe. FYI - the corroded areas of the pipe have whitish salt-like deposits surrounding the pinholes on the outside of the pipe. I found that the pipe had pinholes in it when I used a mechanics pick to examine the corrosion deposits on the exterior. I have not inspected the inside of the pipe as I just found the pinholes tonight.

ScottMP

Cast iron rads

What he means by a cold start is the boiler is cold untill a call for heat. When the thermostate calls for heat, then the boiler starts up. With this design you have alot of cold water from the cast iron radiators coming back into the boiler. Your system may be condensing at low temperatures. All that cold water going thru the boiler while its firing.

I would think the simple solution would be a Buderus conrtol that would allow the pump to shut down when the water temp. drops below 120 and would allow the boiler to catch up. Other solutons would be a primary/secondary near boiler piping or a mixing valve.

Scott

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Steve Ebels

PB

What you have going on there is condensation of the flue gases, which are corrosove in nature. This is what's eating your breeching pipe. A much bigger question is if this is happening in the boiler also. A few $7 pieces of pipe will not fix the problem if this is occuring in the boiler itself.
What happens is that the boiler is relatively cool, especially in the shoulder seasons and it's connected to a system with a LOT of mass. Then when the boiler fires it's working against all that cool or cold water. Water temps below 140 will generally cause condensation in a gas boiler. So until your boiler gets up to temp this condensation is likely happening in your system. Not a good thing!!

An analogy would be that your boiler is like a team of horses starting out a heavy load. They work really hard to get it moving and they sweat when they do this. Once the load is rolling along, they don't have to work as hard and they stop sweating. The same thing is happening with your heating system. It's a system control problem, not an inherent problem with your boiler.

A good solution to your this would be to install Buderus' 2107 control instead of the Tekmar. This control, designed and built by Buderus, is made to work with their boilers. It allows the boiler to operate at safe temps by cycling your system pump off and on. It also turns the water temp up and down based on how cold it is outside and will manage your domestic hot water when you add that. It will also likely increase your system efficiency and protect the investment you made in your boiler.

You have an excellent boiler there. You owe it to yourself to have someone inspect it and see if you need to take this step. This will ensure that it gives you the long and trouble free life it's capable of.

H. Green

You mention a stainless steel liner in the chimney. Do you know what type of stainless - 304, 316, al29-4c? Is it aluminum not stainless?

If the warmest part of the vent, the galvanized connector pipe, has failed you should certainly have the liner inspected as well especially if it was not installed in anticipation of a condensing environment.

Call a certified chimney sweep to evaluate the liner. If it isn't appropriate for this environment it may be pin-holed similar to the galvanized connector. For a local sweep try www.ncsg.org and good luck.

tim smith_2

corroded vent connector

I would also be concerned with the length of the vent connector between the boiler and the chimney flue liner, I there is some fair horizontal distance, change the connector to B Vent. Also make sure the Tekmar low limit setting is 140 degrees to help prevent the condensation at the start.

Boilerpro_3

I would say the boiler is running too cool

as steve described above. However cycling the pump, IMHO, is not very good solution, since on most gravity convertions the radiation runs well below the boiler minimum temp (140F) all or most of the winter and would cause the pump to constantly cycle. This would also put additional cycling stress on the heat exchanger due to the rapid changing of temperatures as the pump cycled on and off. A thermostatic mixing valve on the boiler return, along with Primary/ secondary piping would provide a good solution. Using a variable speed pump control, such as a Tekmar 361, would be an even better solution.

Boilerpro

ScottMP

Boiler Pro

How about a four way mixing valve instead of a Thermostatic valve, which would create flow restiction ?

The four way could run thru a Buderus control and allow lower water temps .

Scott

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Dale

Pinholes

Pinholes in a short time are usually acid, as the moisture dries up into a little puddle in the vent pipe the acid becomes more concentrated. I would suspect anything with chlorine or refrigerant leak or charging a battery or laundry contamination, bleach, dryer sheets ect. You can fix this by bringing outside air directly to the burner area.

PB

Reply

> I would also be concerned with the length of the

> vent connector between the boiler and the chimney

> flue liner, I there is some fair horizontal

> distance, change the connector to B Vent. Also

> make sure the Tekmar low limit setting is 140

> degrees to help prevent the condensation at the

> start.



The total length of the pipe is probably 4-5 feet.

PB

Reply

The total length of the pipe is probably 4-5 feet. The Tekmar low limit is set at 140 degrees.

THX PB

PB

Reply

I will keep the boiler room door shut to keep laundry and other fumes out. Interesting thing is that most of the corrosion is on the top half of the pipe that is at a 45 degree angle! As I think about all I have read - this makes me think flue gas is hot - but not hot enough, and is running along the top part of the pipe - which is relatively cooler, and it is condensing there.

Thanks, PB

PB

Reply

I will have the liner inspected. - Unfortunately - the liner only says stainless - not the grade.

Thanks,
PB

Boilerpro_3

I expect that would work too....

I know next to nothing about Buderus equipment. I use thermostatics (Esbe Thermix)on the boiler return and then pipe the boiler P/S to the system so the system loop and boiler loop always gets full circulation no matter what the valve is doing. Also allows me to use full reset without the expense an injection pump set up ( or 4 way valve). Soooo many possibilities!

Boilerpro

Art Pittaway

Flue size is 8\"?

I am not sure what the btu output of the boiler and waterheater are but if the flue pipe and liner are oversized it is an invitation to condensation. Velocity needs to be maintained as well as capacity. My own house had an 8" flue that I never looked at until one day I touched the pipe and my finger just went right through. When I researched what should have been there I think it was 5" max for the two combined! Used a proper Y fitting and now when the water heater lights there is always plenty of draft.