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 > Tankless Hot Water Heater Troubles

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Buddyg23

Tupelo, Mississippi

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Posted: 06/24/12 08:18pm Link  |  Print  |  Notify Moderator

I had a tankless hot water heater installed in my 2011 Jayco Greyhawk a couple of weeks ago. I was told not to use the cold water to regulate the temperature. Instead you use the flow of the hot water . For cooler temp. you turn the hot water valve all the way open. For warmer you close it off a little. My problem is that this does not work. The temp fluctuates between scalding and freezing. One minute it will be so hot you can't stand it and the next it will be cold. I have taken it back to the installer. He does have any idea whats wrong. Does anyone know a fix for this?





j-d

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Posted: 06/24/12 08:38pm Link  |  Print  |  Notify Moderator

What does the instruction manual say? What is your water source? Are you running from the RV's fresh water tank? Or from a campsite hookup? If hookup, are you using a Pressure Regulator in your supply hose?
I wonder if you have fluctuating supply pressure to your tankless heater.


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Dick_B

Palos Heights, IL USA

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Posted: 06/24/12 08:39pm Link  |  Print  |  Notify Moderator

Here is a website that may shed some light on the problem: http://www.gotankless.com/compare-tankless-water-heaters.html
I am far from an expert but it looks like the temperature control is not the best so I would try to control the ultimate temperature by setting the hot side on a fixed flow and modifying the temperature with the cold side; despite what the dealer said to do.
It can't hurt anything and just might work!


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Golden_HVAC

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Posted: 06/24/12 08:59pm Link  |  Print  |  Notify Moderator

I have written a bunch of reply's to those considering a tankless water heater, and not one was positive. I think the only way I would use a tankless water heater is to pre-heat the water going into my RV, and make the water 80F, so that the person taking a shower will not need much hot water from the 6 gallon tank.

It seems like you have a water heater with a on-off gas valve, not a much more expensive variable gas flow valve, and the electronic controls that measure the incoming water volume, temperature, mid heat exchanger temperature, and output temperature. With the proper controls and a 75,000 Btu gas supply, the heater can take 45F water at 3/4 gallon per minute all the way up to 2 GPM and heat it to 120F instantly. Anything less will not heat the water the way you "Desire" it to be heated.

The best way to make yours work is to keep the water flow high enough to not trip the low water flow switch or overheat switch, and hopefully you will get warm water. I think that you are setting the water flow to low, and tripping the high temp switch, that will shut off gas flow all the way until cold water comes out, then turn on the burner again, heating the water to scalding hot until you trip the high limit again.

How many gallons per minute is your pump? Or if you are on city water, perhaps the shower head is not allowing enough water volume out of the head to keep the water in the lukewarm water temp

I guess you can test the system by running water out of the kitchen faucet, and see when the temperature is going on and off. So adjust the volume for say 110F, and then slow the water flow a bit until it is going hot and cold like your problem in the shower. Then increase the water flow until the point that the water stays warm, say at 90F. So you will need to keep the water temperature between 100 and 110 so that you don't trip the over temp limit.

I think I will get a Ecoboost 5, it is a tankless water heater that is 35,000 Btu's and will be able to preheat all the water going into my RV. Or I will get a 10 gallon hot water tank, (only if I change RV's) so that I can have plenty of hot water. With the 6 gallon tank, and 45F water going into the tank when camping up north, the hot water runs out really soon! Warming the water from 45 to 80 (or even 75) will make a huge improvement in how long the water heater tank will last. Yet it still might have a problem with the water suddenly changing from 80F cold side to 45 cold side if the water heater trips for whatever reason.

I hope I provided some insite to your problem.

Solutions is probably changing the shower head to a higher flow model, or changing the water pump to a 5.7 variable speed pump.

Fred.

Golden_HVAC

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Posted: 06/24/12 09:06pm Link  |  Print  |  Notify Moderator

Another tip, if you want to have slower water flow. Try shutting off the gas supply about 1/8 of a turn at a time, until the gas flow is slower, and the temperature is lower, so that the water is not getting to scalding hot, and tripping the hot water limit, then going cold for a few seconds.

Fred.

donn0128

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Posted: 06/24/12 08:48pm Link  |  Print  |  Notify Moderator

Do a search for tankless woos on this or any other RV forum will turn up all sorts of complaints. Sorry you missed the previous posts as it probably would have saved you a lot of money and grief. Try and return it and get your money back and install a standard water heater.


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Westronics

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Posted: 06/24/12 11:04pm Link  |  Print  |  Notify Moderator

Wow... this used to be on my wish list, but I think I'll strike that item. I have yet to hear of one working well in an RV.


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Jim Cindy

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Posted: 06/24/12 09:06pm Link  |  Print  |  Notify Moderator

We don't have a tankless in our Cameo, but we do use one at our Family and Friends Camp for the outside shower and sinks. We turn the hot on full and adjust the temp with the cold. A sufficient flow of water thru the heater must be maintained in order for it to work properly. If you try to control the temperature with the hot side it reduces the flow and the heater will shut down.


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Normk

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Posted: 06/24/12 09:31pm Link  |  Print  |  Notify Moderator

Fred has nailed much of the issue with demand type heaters. We used one for years at our cottage so am quite familiar with some types.

First thing, IMO who ever told you to use the hot water flow rate to regulate temperature has it backwards. You need to use the cold water flow to control temperature.

Demand or tankless heaters are water heaters which can heat the full flow of water to a hot temperature. They have big burners/heaters and heat the full flow volume of water so that they don't need to store a volume of water and gradually heat that to the set temperature.

When using a demand heater, the big thing to understand is that they only work when flowing at full rate or close to it. Turn the water on, full flow and you will hear the heater kick in and hot water will flow. The tank has a water flow "sensor" which detects that water is flowing at the desired rate (basically full flow) and starts the burner. After a short time the burner has succeeded in reaching temperature and the hot water flows until the unit is shut off.

Problem is, if you don't start the water flow to a high enough rate, the burner won't light/turn on so all you get is cold water. Slow the flow too much through the demand heater and it turns off the burner so all you get is cold water. The only way to use these is with the hot water tap turned on 100% flow. If the water is too hot, increase the cold water to dilute the hot to desired temperature. Seems simple enough, right?

Now here are some more problems which can be introduced:

Low flow, economizer shower heads or aerators at the sink will reduce water flow so that there is not enough water flow to keep the demand "sensor" open and the burner shuts off = cold water. It is common for people to install these units and have full temperature hot water only available because adding cold water to dilute the hot, adds to the flow through the low flow shower head or sink aeroator and slows the flow too much for full flow through the heater.

Another problem is the same as above excepting that this is that the piping in the system, or part of the system is too restrictive to allow the demand to have enough flow so it may fail to provide any hot water to one or more faucets or may turn off as soon as any cold is added.

Again another issue is on the supply side to the demand heater if the pump is too small in volume to maintain sufficient pressure & flow to keep the demand going. Again, there can be a great enough flow for hot water but as soon as there is a demand for some cold to dilute, the flow through the demand my diminish enough to shut down the heater.

In the shower and have the ht water open 100% flow, then add cold to set temperature and then someone opens another faucet- WHAM! 100% cold water or too hot! This is usually much more pronounced than in a conventional system.

At our cottage, the only way to stabilize the water temperature in the shower was to add a bleed line with valve to flow some of the mixed water to the floor of the shower in parallel with the shower head in order to provide sufficient flow.

Don't know if this helps but there are many possible issues with your system and the solution will require someone there with an understanding of these systems, who can do pressure tests and flow tests in order to determine the root cause. People who tell you, "It's this...", or "It's that..." don't know of what they speak. These systems can be the best thing going but for small scale useage they do require operator understanding of the system in question as each will be a bit different.

Someone's comments regarding the issues with differing supply water temperatures points out another problem variable. We noticed large differences in how the shower needed to be operated and learned to make appropriate settings to the number of burners operating and other factors in order to partially compensate for different water supply temperatures.

Another system with which I worked, was almost 100% stable at all useages (hot water on 100% and adding almost any amount of cold to control) while another would drive the crew crazy until it was learned that filling the water tank from shore supply was providing much colder water than was available during most of the voayage. Everyone avoided showering for the first shift after departure and there were no problems.

I am sure that the installer is pulling his hair because he was likely told that the installation was straight forward but now he has a bear by the tail. Try to keep in mind that he was likely also caught unawares and try to work together to solve. Pressure & flow rates need to be considered.

Please advise as to how you are getting on. Wish you were close by as could likely help out. At least being retired with time and a power engineering certification, might be able to find a solution which your installer, who has a living to earn, may not have time to do.

All58Parks

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Posted: 06/24/12 11:22pm Link  |  Print  |  Notify Moderator

Westronics wrote:

Wow... this used to be on my wish list, but I think I'll strike that item. I have yet to hear of one working well in an RV.


No kidding. I wondered why I never heard of them in RV's, they seemed prefect. Now I know.


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