Carbon clogging propane water heater

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Old 09-29-20, 01:12 PM
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Carbon clogging propane water heater

I have a newer high efficiency water heater running on propane. It will light but immediately go out. I pulled the bottom cover off and the combustion chamber is filled with carbon. There is airflow coming out the pvc flue, but that has a lot of carbon in it as well. I’m thinking that the first thing that needs to happen, before trying to get the flame right, is to clean the carbon out of it. But how? I’ve brushed boilers before but I’ve never seen a water heater that looked like an unmaintained boiler.
 
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Old 09-29-20, 01:18 PM
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Was this purchased as a propane water heater or was it converted from natural gas ?
If you have a carbon problem...... there is too much fuel and not enough air,
 
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Old 09-29-20, 01:29 PM
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The energy guide says propane. I spoke with the guy who installed it. He’s now retired. He’s sure he set it up right. He has someone else he can recommend , but he’s guessing they will recommend replacing the unit. I’m sure I can get the flame right, but how do I deal with the carbon. It has to be blocking passages.
 
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Old 09-30-20, 05:04 PM
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In case anyone is following, I pulled the burner out and it was covered in carbon. I cleaned it, the rest of the combustion chamber, and the bottom of the flue as far up as I could. I put it back together and it works fine. One problem though. The top of the burner, aside from being covered in carbon, was wet. Is there anything besides a leaky tank that would cause this? The water heater is still under warranty so it could be worse.
 
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Old 09-30-20, 06:17 PM
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You need to find what is causing the carbon buildup. It's either too much fuel or not enough air.
You cleaned the unit but without making changes.... it will clog again.
 
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Old 10-01-20, 04:49 AM
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Just for comparison my 18+ year old propane water heater has never been cleaned and has no carbon buildup. Getting carbon is a definite sign that something is not right.

When propane is burned it produces a lot of water vapor. As the hot exhaust gasses rise the cooler water entering the heater causes the water vapor to condense out into liquid and drips back down.
 
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Old 10-04-20, 10:30 AM
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You might want to have someone (propane supplier?) check the incoming pressure with and without the burner firing, and the manifold pressure with the burner firing. Might be a pipe sizing problem, or the installer didn't check/adjust pressures as required.

If there are other gas appliances, see what changes when everything fires.
 
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