Bad tankless coil cause overheating?


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Old 10-07-18, 08:33 AM
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Bad tankless coil cause overheating?

Oil boiler is 16 yrs old with orginal coil. Hot water has been lacking for a couple years now, I assume poor heat transfer. Flushed the coil with that solution last year and got a slight improvement. Sometimes over the past year, the boiler would overheat to 230 and the baseboard had popping sounds, probably steam. I replaced the aquastat thinking the high limit switch was bad and the problem remained. Could an old, tankless coil with bad heat transfer cause the boiler to overheat? I'm not sure what else could cause this.

Thanks.
 
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Old 10-07-18, 10:47 AM
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Once in a blue moon I had to use something like this to get hot water from a standing coil.Maybe your aquastat well is scaled on the outside. Good luck.https://www.comstarproducts.com/boil-a-coil-16-ounce-12
 
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Old 10-07-18, 10:50 AM
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It sounds like the aquastat is not registering the actual water temperature. That could be from corrosion built up on the well inside the boiler. The tankless coil will not cause the boiler to overheat.
 
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Old 10-07-18, 10:58 AM
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If you say the aquastat probe well can make it overheat, then wouldn't that mean the coil in effect is making it overheat, since they are all one piece? Sounds like only remedy is to replace the coil.
 
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Old 10-07-18, 11:06 AM
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The boiler is a tank of water. The well sits in that hot water as well as the tankless coil. As DHW is used.... cold water enters the coil and it will always be cooler than the tank temperature.

The aquastat monitors the boiler water temperature. It doesn't care if there is a tankless coil there or not.
 
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Old 10-07-18, 05:52 PM
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I get that, but in this case it is in the coil, so to fix a probe well issue, don't you have to replace the coil?
 
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Old 10-07-18, 06:06 PM
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No you don't. The well just unscrews from the coil plate. You must drain the boiler below the location of the well because when you remove it the boiler water will drain from the open hole.

http://www.supplyhouse.com/Honeywell...Well-3712000-p

They also come in 3/4" which you can find on the same sight.

Hope this helps a little.
 
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Old 10-11-18, 08:18 AM
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Replaced the coil last night. I see what you mean about the threaded well. The probe well looked pretty clean, but the boiler doesn't overheat anymore, so I'm not sure how a new coil fixed that. But the hot water is awesome now.
 
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Old 11-12-18, 05:28 PM
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If flushing the coil only improved the hot water a little and replacing the coil improved it a lot then the coil still had a lot of lime or other sediment inside.

The probe attached to the coil mounting plate was probably malfunctioning, continuing to call for heat long after the boiler went above its usual temperature.
 
 

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