Momentum "Broccoli smell" coming from furnace vent

[UltraRun1738]

Hey y'all, we just got our Momentum 410THR and have been in it for about 10 days. 2 times now, we have gotten the black tank of the main bathroom (black tank 1) up to about 1/3-1/2 full and at that point a broccoli smell comes in from the furnace vent (which is on the wall between the living room and the bathroom toilet.

The smell gets worse when we turn on a fan vent and try to "negative pressure" the smell out. It just pulls more of it in through the furnace vent.

The smell goes away when the tank is dumped, which makes me think this is a black tank issue, not a furnace issue.

Anyone ever seen this before? The smell doesn't appear to actually be coming up through the toilet, and we are not getting a "burp" nor is there any smell coming from under the sinks. Curious if this is a faulty black tank vent issue or what else can be done to have a permanent fix.

[DougW9876]

A black tank venting problem would be my first guess.

You could go buy some of the orange or citrus scented tank deodorant and put that in your black tank to see if the smell changes next time you get the tank up to 1/2 full.

[SolarPoweredRV]

Hey y'all, we just got our Momentum 410THR and have been in it for about 10 days. 2 times now, we have gotten the black tank of the main bathroom (black tank 1) up to about 1/3-1/2 full and at that point a broccoli smell comes in from the furnace vent (which is on the wall between the living room and the bathroom toilet.

The smell gets worse when we turn on a fan vent and try to "negative pressure" the smell out. It just pulls more of it in through the furnace vent.

The smell goes away when the tank is dumped, which makes me think this is a black tank issue, not a furnace issue.

Anyone ever seen this before? The smell doesn't appear to actually be coming up through the toilet, and we are not getting a "burp" nor is there any smell coming from under the sinks. Curious if this is a faulty black tank vent issue or what else can be done to have a permanent fix.

To determine that it is in fact coming from the black tank, the next time you smell it and you turn on your exhaust fan, open the toilet bowl and check to see if the two smells are the same. If they are not, you might have a Propane leak than only manifests itself when the black tank is one half full. Maybe, the added weight of the tank is putting pressure on a Propane hose, or the furnace is being pulled down and causing a hose to leak.

To check if it is a Propane leak, the next time you smell it and the smell does not match the black tank smell, turn off the Propane tanks and light your stove to remove any pressure in the line, then check the vent if the smell goes away, you have a Propane leak that needs to be checked out ASAP!

Please let us know what you find.

[UltraRun1738]

To determine that it is in fact coming from the black tank, the next time you smell it and you turn on your exhaust fan, open the toilet bowl and check to see if the two smells are the same. If they are not, you might have a Propane leak than only manifests itself when the black tank is one half full. Maybe, the added weight of the tank is putting pressure on a Propane hose, or the furnace is being pulled down and causing a hose to leak.

To check if it is a Propane leak, the next time you smell it and the smell does not match the black tank smell, turn off the Propane tanks and light your stove to remove any pressure in the line, then check the vent if the smell goes away, you have a Propane leak that needs to be checked out ASAP!

Please let us know what you find.

I ended up playing around with the sewer hoses to clean a few things up and get better flow - I can verify that the smell is the same in the outflowing sewer hose as is what’s coming in via the furnace vent.

The smell hasn’t come back yet but just waiting for it

[FT4NOW]

It's possible the vent or toilet discharge pipe isn't sealed all the way. It's certainly under warranty if you don't mind waiting for whoever knows how long. GD will authorize mobile techs to perform warranty work, or you can try to get a look at the top of the tank yourself which would require dropping some of the underbelly. Other possibilities could be there is a leak where the tank sensor is installed, tank valve leaking or cracked tank, that pretty much sums it up. For all of those possibilities it would require the underbelly to be dropped for inspection.

One other possibility, the vacuum breaker on the black tank flush line could be bad and allowing odor into the people space. I'd investigate this first as it is the least intrusive and they are known to fail.