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5th Wheel Trailer Can't Have Heat and Hot Water At Same Time

by David Mullins
(McAlester,ok)


My mother in law lives in a Fifth Wheel on an RV pad I built for her a couple a years ago. She has started having problems with her central heat kicking off when the electric water heater is turned on or if she turns on her lights more than one at a time, could this be a converter problem or even a battery problem?

It has been parked here for two years.

ANSWER: Hi David thanks for submitting your question on our Ask An RV Question Page.


Yes, what you describe could be caused by the 5th wheel's Electric Converter. Also based on your description there may also be problems with the house batteries as well.

The heating element on your RV's water heater should be powered by 120 volt AC and the blower motor on the furnace runs on 12 volts DC, so turning on the water heater should have no effect on the furnace at all.

The lights built into the RV run on 12 volts DC and if they are getting dim when more than one is turned on at a time that could be a problem with the Converter or even the House Batteries. If the converter is not properly providing 12 volt DC to the RV having more lights on may also affect the furnace blower motor. When the 5th wheel is plugged into shore power the Converter should be providing the 12 volt DC power to the RV and at the same time charging your RV's house batteries.

Since this RV has been plugged in for two years straight I am assuming that someone has been checking the house batteries at least once a month as the batteries have been receiving a constant charge for two years and depending on the type of charger built into the Converter; the house batteries could be boiled out. Please follow the steps below.

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1. Check the electrolytes in batteries and top them off with distilled water as needed.

2. Check the batteries for loose connections and clean any corroded battery connections.

Now it is time to check to see if the Converter is properly charging the house batteries.

I am not sure if
your RV has a panel that shows a digital reading of the voltage going into your house batteries. If it does; follow the steps below to see if your house batteries are being overcharged. If your RV does not have a digital readout then you can use a simple voltmeter to get the voltage readings at the house batteries.

1. This step requires that the RV be unplugged from electric. go through your RV and make sure that all of your 12 volt lights, etc. are turned off. Then go to the panel that shows the battery voltage or use your voltmeter and see if the batteries show any charge at all. If they show any charge at all regardless how low, go ahead and move on to step 2.

2. Plug the RV into electric. Take a look at the battery voltage reading. If the charger is working properly the reading should be around 14.4 volts + or - .2 volts. If the reading is too high then it means that the charger built into the RV's converter is overcharging your batteries; If the voltage reading is low; it would mean that the battery charger was undercharging the batteries or not charging them at all.

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3. The last step is to go into the electrical compartment of the trailer and check for any blown fuses or tripped circuit breakers.

Once you have done all of the above try operating the lights, water heater, and furnace all at the same time and see if you experience the same problems. If you do then you need to have the Converter checked out by a Certified RV Technician as there are no user serviceable parts in the Converter and I highly recommend that you do not attempt to open it up and try to fix it.

Hope this helps.

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Happy RVing

RVing Al

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Comments for 5th Wheel Trailer Can't Have Heat and Hot Water At Same Time

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by: Bill A

Yes you pretty well covered it,lots of people neglect to check the batterys,sometimes the battery boxes fill up with water and causes corroshen,but if it is plugged into shore power everything should work,no matter if it has no batterys at all,yes check fuses first sounds like a ground problem also.Got to have good clean ground connections,every ground wire you can see.

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