Viessmann Vitodens 100-W: Radial Fan Air Intake Port Deteriorating / Wearing
Hi Viessman Experts,
We have a Viessmann Vitodens 100-W propane furnace and the Radial Fan NRG118 air intake port deteriorates to the point where it drives F4 errors and has to be replaced. Also noticed fouling on the it's burner interface flange. Seems like the burning propane flame is somehow backing down the input channel which I can't imagine is intended. Please see the photo's below.
Any thoughts on why this is happening would be greatly appreciated, we are now on our 2nd fan replacement in 6 years!!!
Thanks, Paul
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Just worked on one today with same issue. Code F4 I'm a 4 year old boiler. Wont ignite. Inlet looks the same. Is replacing fan only option? Trying to see what caused this
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It's flue gas recirculation. the flue gasses are re-entering the cabinet and being sucked in to the fan. From my estimation that is really extreme. I've seen at least a hundred jobs where there is considerable flue gas recirc on these boilers and never seen the venturi wear down like that, seen plenty of the "paper" style venturis break down. In the bottom left of the inside of the cabinet there is probably a big brown or black spot like rust sort of. The cure is to separate your vents, the intake should be pulling in fresh clean air only and be separated from the exhaust, not just to manufacturers minimum separation it needs to be separated enough that it doesn't recirc.
If you really think it's the flame getting sucked out of the fan you can always pull the burner and have a look. My guess is that its not pretty in there! The burner should get pulled out and everything cleaned and put back to factory spec annually (every other year realistically.)
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So the boiler was plugged into a receptacle for a near by humidifier. That plug only had power when the furnace blower was on. So power was getting cut mid heat cycle and flue gasses just hung around in the fan and cabinet and ate away at the venturi. Replaced fan and ran a cord to a proper receptacle
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No post fan purge. It is a one pipe vent system.
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It's flue gas recirculation. Check the condensate drain where it goes into the trap. If there is any debris at that connection it might leak flue gas.
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Hi @gibbs05, Hi @R Mannino,
I'm just seeing these comments, very interesting! I haven't resolved my issue so will investigate your suggestions. I did have someone question if the gas pressure is too high. There isn't a gage on this system so I don't know what it is. Does anyone know if there is a pressure specification? Thanks, Paul
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Its not a gas pressure issue… plain and simple Its a flue gas issue.
The exhaust is getting sucked back into the intake.
I have seen this plenty of times w/ several different makes/ models.
This Is one of the main reasons I dont like concentric / single pipe set ups.
Show us a pix of the termination outside.
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If this condition exists, there are more immediate concerns such and carbon monoxide entering the room.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
Hi @kcopp, Hi @Alan (California Radiant) Forbes, thanks for your feedback! I won't be able to take pictures until this weekend but I will of the exhaust and unit.
By the way, it is frequently windy at this house and the exhaust is exposed. I have wondered if wind may be blowing exhaust back into the unit.
Also, I've cleaned the plastic condensate trap that is inside the furnace but haven't checked the drainage path from that unit. It goes into a reservoir / pump device which pumps into an open drain in the floor. I'll take a picture of that too. I have notice the system accumulates a fair amount of moisture which I always thought was odd. Perhaps there is an obstruction somewhere and water is backing up.
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the moisture should drain in to the condensate pump or possibly also run out the exhaust depending on how the exhaust piping is pitched. When the gas burns about half the gas produced is water vapor and a condensing boiler is designed to condense that back in to water and bring it out a condensate drain if the operating conditions are favorable to condense the water vapor.
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Hi @mattmia2, thanks for the explanation. The exhaust pipe goes straight up for a couple of feet then horizontal for perhaps up to 6 feet. I'll check the horizontal part to see if it is pitched back towards the house causing all the condensate to drain back into the furnace possibly accounting for what seems to be abnormal amount of moisture in the main body of the unit.
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The pipe is supposed to pitch back toward the boiler, all of the condensate is meant to drain back to the boiler and out the condensate drain. All of that pathway needs to be clear so condensate doesn't build up, it should all drain free. Take photos inside the fire side of the heat exchanger, it should be clean and drain freely.
Take photos of your vent terminations, if the exhaust and intake are close it can recirculate.
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Hi @GGross, understood… will take pictures this weekend. Thanks, Paul
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Hi @gibbs05, @GGross, @mattmia2, @kcopp, @Alan (California Radiant) Forbes,
Here are some pictures of the furnace. The intake is just the hole in the top and the exhaust goes out the wall and through several deck joists so can't be moved if the condensate pitch is not proper. Unless the exhaust is leaking where it leaves the furnace, I don't see how it could be recirculating exhaust… not sure how to tell if it is leaking. Thanks for any suggestions, Paul
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Well, one thing we know is recirculation is not the issue as your combustion air is coming from indoors.
The exhaust should be pitched with the low end at the boiler. When the boiler runs water is going to condense, and it will come out either the end of the exhaust outside or drain back to the boiler (which is the correct pitch) and come out the condensate drain. Make sure the condensate path from the boiler to the drain is clear.
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that looks like a long outdoor run, how long is that deck/run? any concerns about condensate freezing in what looks like might be a flat run? and freeze plugging the run?
Where are you? How cold do you get there?
known to beat dead horses0 -
Boiler.
Not a furnace. Its hot water not hot air.
It dose not look like there is much if any pitch on the vent.
Should be 1/4" per foot.
There should be an air intake from outside. (yes its allowed but not a great idea.)
You could very well not have enough combustion air or contamination from chemicals inside.
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unless the connector or hx is leaking in to the cabinet and being pulled in that way
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Hi @EBEBRATT-Ed, surely looks like recirculation is not the problem unless there is an exhaust leak near the intake. Perhaps we should install an alarm nearby to see if it detects anything. Also, the condensate pitch appears to be non-existent and the drain out of the boiler is clear.
Hi @neilc, the house is in upstate NY so gets pretty cold in the winter. The exhaust pipe is a fairly long run, perhaps 8' to 10' (I'll measure next weekend), and freezing condensate is an interesting thought which probably happens to some extent. Both makes me wonder if there is significant resistance to the flow, would it affect / reduce the flow of propane from the Radial Fan enabling the burn to back up from the chamber towards the fan? Perhaps I should shorten the exhaust pipe and let escape under the deck or I think we might be able to move it next to the propane source pipe closer to the house that you can see in the picture of the exhaust exit port.
Hi @kcopp, the space under the deck is limited so rerouting the exhaust would be very difficult if not impossible. What happens if there is incomplete combustion? Would it just impact the efficiency?
Hi @mattmia2, I agree, a leak where the exhaust escapes the boiler is a possibility but if it is, I would think it is a very small amount. The fuel is propane so not sure if we would smell anything.
Thanks for all for your feedback!!! ….Paul
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