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Old 15-07-2019, 10:42   #1
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Hot water heating element keeps failing

I rarely am at a marina so I normally don't use the 110 VDC hot water heating element. But on occasion I do want to but the element keeps failing. Let me explain.

About a month ago I had installed a new heating element in the Isotherm 8 gallon hot water heater. I used it for 3 weeks at the marina without any problem. Then I turned it off and motored for 11 hours to a new location/marina. When I tried to use the hot water heater it did not work.

This has happened three times Ö new heater element Ö works Ö go sailing Ö hot water element is bad.

At first I thought that the failure had something to do with the pounding at sea though that should not make a difference, but on the motor trip to a new marina the seas were near dead calm.

Do you have any idea what is causing my problem?

Marcus
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Old 15-07-2019, 16:30   #2
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Re: Hot water heating element keeps failing

Have you checked all of your wiring connections and inspected the terminals? What is the resistance value of the heating element? You may be replacing the heating elements but the problem may be in the wiring. Just a SWAG.
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Old 15-07-2019, 16:34   #3
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Re: Hot water heating element keeps failing

When you say it went bad what do you mean? If it’s that it doesn5 come on after motoring is it that 5he water is already hot? My hot water gets a LOT hotter off the engine than the electric heater.
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Old 15-07-2019, 18:30   #4
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Re: Hot water heating element keeps failing

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Originally Posted by sailorboy1 View Post
When you say it went bad what do you mean? If itís that it doesn5 come on after motoring is it that 5he water is already hot? My hot water gets a LOT hotter off the engine than the electric heater.
No. After motoring I don't turn on the water heater until the hot water gets used up. Then it does not heat the water.
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Old 15-07-2019, 18:32   #5
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Re: Hot water heating element keeps failing

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Originally Posted by sailorboy1 View Post
When you say it went bad what do you mean? If itís that it doesn5 come on after motoring is it that 5he water is already hot? My hot water gets a LOT hotter off the engine than the electric heater.
What I mean is that after motoring, then using up the hot water in the tank, I then turn on the electricity and the water will not heat.

I plan to call Isotherm to see what they think. They might have an idea.
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Old 15-07-2019, 18:52   #6
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Re: Hot water heating element keeps failing

When you replaced the element, did you also replace the hot water thermostat which is usually fitted into the element.
Could be that the thermostat is set to trip at a temperature below that of the engine coolant water (when engine hot). So with engine running and heating the hot water, the thermostat trips and when you plug into shore power, no power will go to the element.
Most thermostats will have a reset button so try resetting.
If that solves the problem, then get a new thermostat which wont trip at the engine coolant temperature
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Old 16-07-2019, 09:15   #7
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Re: Hot water heating element keeps failing

Heater elements are very sensitive to over voltage. Have you measured the voltage at the heater terminals? Is the heater element the correct voltage for your system?
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Old 16-07-2019, 09:40   #8
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Re: Hot water heating element keeps failing

Have you checked to see if amperage increases when adding power to the heater? Have you checked resistance on elements after they stopped working? Is the element always submerged in water when power is added?
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Old 16-07-2019, 13:50   #9
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Re: Hot water heating element keeps failing

Is the element burned out? Or did it just not heat up as in no electrical current going to it?

I know from experience that if the water level isnt high enough in the tank, or if you are using more water than is being replaced by your pumps that the 110v element can burn out as its not made to run in a dry environment. It must be submerged in water all the time its on.
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Old 16-07-2019, 14:35   #10
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Re: Hot water heating element keeps failing

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Heater elements are very sensitive to over voltage. Have you measured the voltage at the heater terminals? Is the heater element the correct voltage for your system?
Hmmm.

Heating elements are just a dumb resistance load. As long as the element is immersed in water it cares little for what voltage it sees. Within limits.

P=VI where heating capacity in Watts is dependent on Volts multiplied by Current in Amps.

Is there a breaker or thermostat in the OPs system. Are you checking the element for open circuit before replacing it.

Do you have sufficient power (Volts x Current)? Any bad connection will sigificantly reduce the voltage and therefoe power.

Its not uncommon to burn out connections, breakers and fuses in heating circuits due to the high current.
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Old 16-07-2019, 15:01   #11
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Re: Hot water heating element keeps failing

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Originally Posted by nigel1 View Post
When you replaced the element, did you also replace the hot water thermostat which is usually fitted into the element.
Could be that the thermostat is set to trip at a temperature below that of the engine coolant water (when engine hot). So with engine running and heating the hot water, the thermostat trips and when you plug into shore power, no power will go to the element.
Most thermostats will have a reset button so try resetting.
If that solves the problem, then get a new thermostat which wont trip at the engine coolant temperature
This ... my friend had one of these heaters and it would do this all the time - you could reset it , but it was a hidden reset button if I remember correctly
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Old 18-07-2019, 11:25   #12
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Re: Hot water heating element keeps failing

Thanks for all the suggestions. The problem is related to the fact that the hot water generated from running the engine is much hotter than from heating the water electrically. What happens is that if I turn on the power to the hot water heater before it cools partially after running the engine, then the thermostat internal breaker activates. I can manually reset the breaker on the thermostat. The solution in the future is not to turn on the power to the hot water heater until the temperature drops after running the heater.
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Old 18-07-2019, 14:29   #13
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Re: Hot water heating element keeps failing

You should be able to get a thermostat with a higher rated trip temperature.
Thermostats I have seen will trip irrespective of whether the element has power going to it.
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Old 18-07-2019, 17:23   #14
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Re: Hot water heating element keeps failing

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You should be able to get a thermostat with a higher rated trip temperature.
Thermostats I have seen will trip irrespective of whether the element has power going to it.
I was wondering if it could trip without power. Thanks for insight. It takes about 5 seconds to reset the thermostat so Iíll probably stick with what I have for now.
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Old 18-07-2019, 17:25   #15
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Re: Hot water heating element keeps failing

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Originally Posted by mlibkind View Post
Thanks for all the suggestions. The problem is related to the fact that the hot water generated from running the engine is much hotter than from heating the water electrically. What happens is that if I turn on the power to the hot water heater before it cools partially after running the engine, then the thermostat internal breaker activates. I can manually reset the breaker on the thermostat. The solution in the future is not to turn on the power to the hot water heater until the temperature drops after running the heater.
Thanks for the feedback.
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