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Old 10-08-2012, 12:09   #1
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Hot Water Heater Overheating

My hot water heater has a heat exchanger fed from my engine as most do. The problem is that my engine runs at 180-185 (normal temp) degrees and the pressure relief valve on the water heater is rated at 180 degrees and opens from time to time. Is there a way to either by pass the water tank heat exchange when the water temp gets to about 150degrees or automatically shut the feed down?
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Old 10-08-2012, 12:17   #2
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Re: Hot water heater overheating

You can restrict, with a metering valve, the amount of coolant flowing to the heater loop.
How, and where, you install the valve, will vary on different motors.
Make sure that you don't restrict the flow necessary to cool the motor.
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Old 10-08-2012, 13:39   #3
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Re: Hot water heater overheating

Restricting the flow to the water heater from the engine will only make a difference if you don't run the engine very long.

Do you have an expansion tank in the fresh water system as this should accept the pressure from heating up the water heater.
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Old 10-08-2012, 20:30   #4
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Re: Hot water heater overheating

Dons right.. could be thermal expansion. You'll want one if you don't have one for the expanded water caused by engine heating.

The relief valves on all waterheaters (in the US anyway) have a T&P (temperature and pressure) relief. So excess pressure will open the relief too.

Two quick options come to mind. one install a 170 degree T stat on the engine.

Could rig a temperature control with a normally closed asco 12V solenoid interlocked with the engine ignition so the solenoid opens when the engine runs and the water temp is below 150-160.

Some of the water heater manufactures also sell a non-powered temp control, but not sure if its sold seperate from the water heaters..
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Old 11-08-2012, 07:21   #5
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Re: Hot water heater overheating

Thanks sailorchick,
I am going to see if I can find a 160-170 degree t stat.
Perkins is a 180 but I might match one from a auto parts place that will fit an have a lower temp. The easier the better as you know space is at a premium in an engine room and the fewer fittings and hoses the better.
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