Hot for three seconds...


Old 07-25-07, 12:19 PM
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Hot for three seconds...

Whenever I turn on the cold water it is cold then three seconds later it is boiling hot for about 2 seconds then runs cold again... Why woudl lis be? I have one of those new furnaces that run off the hot water tank (oil) and I have it turned to the minimum setting for hot water. I checked all the plumbing to see if there was a mixup but everything seems fine. My only guess is that right when the hot and cold feed into the water heater from the main source, there is a line that runs from the hot water line to the cold line and where it is attached to the hot water line there is the switch to regulate how hot the water is. (am I clear enough) I live very far in the bush in northern ontario so it is hundreds of dollars just to have a tradesman come here. not to mention the work. anyway I hope this is a simple problem. I tried turning up the hot water and it seemed to shorten then length of time the cold water runs hot. I am not sure what do to. Any advice is great! THanks

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Old 07-25-07, 04:02 PM
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Without seeing your plumbing, this is just a guess, but I mapped out a scenario quickly, and this could be what happens: For some reason, hot water is expanding or otherwise getting a ways up your cold feed line to your combo water heater boiler. The now hot water in your cold supply line Is now up the cold line too far, and beyond a T-fitting where the cold water supply can either go to the boiler/water heater or go the other direction to your faucet.

Draw this diagram on a piece of paper:

Draw a large T. The vertical line represents your main house feed of cold water before it either goes to the water heater/ boiler to the left, or your faucet to the right. Now imagine that the water heater hot water expanded and traveled back along the left horizontal line to beyond where it crosses the T. Now, when you turn on your faucet, you will still get some cold water. But now because there is some hot water trapped in the line to the right of the T, you will then experience hot water coming out of the faucet until the cold water takes over completely. Follow that? Did you draw the diagram and see how this could be?

Now here is the reason why this MIGHT be happening. You may have an expansion tank with your combination boiler/water heater. The expansion tank may be water logged. When the water heater or boiler gets hot, then the water tries to expand and push out into the cold water line to go up the cold supply line where there will be less pressure. If my guess in all this is right, you need to find the expansion tank. See if you have one. It will be either a possible torpedo looking thing that could be either standing upright near the water heater boiler or suspended from the ceiling, or, it coud be a colored tank that resembles a propane tank used for gas grills. If you find such a tank, post back here and tell me, as this tank could be the key to your problem.

All of this is just a guess. But it just might be a good guess.
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