How to patch an inaccessible vent pipe
Full replacement is impossible when a damaged vent pipe sits hidden between a floor and an exterior wall, forcing a repair from the inside instead. Standard exterior patching products often crack repeatedly within months, leaving homeowners stuck searching for a durable solution that holds up on hard-to-reach connections.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Attempting to patch the pipe in place without replacing the damaged section.
- 2Asking online communities for alternative products to recommend to the contractors
- 3Using Xypex fast setting crystalline quartz patch
- 4Cleaning out the hole and using hydraulic cement on both sides
- 5Removing the failed caulk and applying Quikrete patch with spray paint finish
- 6Doing the repair work yourself instead of relying on hired contractors
- 7Calling a chimney or HVAC professional to inspect and provide a quote
- 8Attempting to patch or replace the stack as a seasoned DIYer
In their words
Unedited, most upvoted first, each linked to the thread it came from.
“Had a power vented hot water heater put in last year and the product used on the exterior keeps cracking.”source ↗
“The company has come out to redo this twice now but there surely has to be a product that doesn’t crack within 3 months.”source ↗
“Frustrating that I have to recommend something to the people that are supposedly the experts but here I am.”source ↗
“Can it be patched or replaced easy without digging into the roof as an seasoned diy-er or needs hvac professional due to carbon monoxide concerns?”source ↗
“So basically, replacing this coupling is really not an option because there is no access it is right in between the floor and exterior wall. I need to patch this somehow.”source ↗
“This was found this way when I got the house”source ↗
Where this came up
People with this problem also raised
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- 2How to find replacement parts for a rusted water heater vent pipe
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- 2How to fix a PVC drain pipe broken flush against the wall