Oil boiler doesn't provide hot water for more than a minute


Old 12-23-16, 08:09 AM
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Oil boiler doesn't provide hot water for more than a minute


Hoping someone can give me an idea of what can be done in my mom's system. They tend to live with lukewarm showers, however I would like to help them out. They are pretty frugal so they are waiting for the whole system to go bad before they want to spend money.

Here are pictures of their setup. I *think* it's a internal coil for the hot water...but I am unsure of what the tank hanging in the rafters is for.

thanks in advance for the help.

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Old 12-23-16, 09:37 AM
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Around here, many people need to have their tankless coils flushed with an "acid treatment" to reduce the mineral deposits which impeded heat transfer . . . . I don't know if that's your Parents' problem ? I have hard (heavily mineral laden) water, and my tankless coil has never needed this treatment.

Meanwhile, the tank up in between the floor joists is expansion tank for the boiler water (NOT the domestic hot water) and it may or may not still be in use. Many are replaced with a diaphragm type expansion tank and they abandon the old tanks right where they are hung.
Old 12-23-16, 05:46 PM
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As Vermont explained tankless coils have a tendency to lime up and hamper the heat transfer from the boiler to the coil. That is why you initially get hot water because that is the water sitting in the coil of a boiler full of hot water but when the water is turned on and fresh cold water comes in it doesn't have a chance to heat up because of the mineral laiden coil.

You also have a mixing valve there that might be bad preventing the mixing of hot and cold water. There is a replaceable element in that mixing valve by unscrewing the top it can be replaced without soldering in a new valve.

What you can do is have someone turn on the tub because that is your biggest draw and you stand at the coil and put your hand on the hot water pipe coming from the coil before the mixing valve and see if it stays hot. If it starts to cool after a few minutes then you know it's the coil and not the mixing valve and it must be cleaned or replaced. If that stays hot feel the pipe coming from the mixing valve to the faucets and see if that's hot. If not it's the element in the mixing valve.

Although the boiler is old I wouldn't replace it just because of the coil.

One more thing to check is the temp of the boiler. If the aquastats are set to low that will affect the coil also.

Your expansion tank in the ceiling is in use but that has nothing to do with your problem.

Hope this helps a little.
Old 12-24-16, 02:15 PM
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Thanks for the info! I will check out the mixing valve this weekend. Hope you both have a happy Holiday.

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