Suburban RV water heater boiling over

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Smoky

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I have a 2005 Kountry Star diesel 3910 model and installed is the Suburban RV water heater.  This water heater uses electric and gas for heating the water, providing both options.  The heater began boiling over at the relief valve, dripping hot water down the side of the coach.  Initially this occurred when heating by electric, but now it does this with either electric or gas option.  I assume that this might be because the thermostat is not shutting down the heaters at the right time.  And on rare occasions we have also had times where the water is not fully heated.  But more often it is overheating the water and boiling out through the relief valve.

Is there a way to troubleshoot this to be sure of the problem.  And if it is the thermostat (or some other problem) is this user fixable?  It is under warranty but rather than go through that hassle, if I can fix it myself I would prefer that.

Any tips or suggestions?
 

Ron

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Most likely you don't have enough or possibly no air space for expansion.  with the water source off drain the water heater down about half full leaving a hot water tap open or opening the relief valve to allow air to enter the tank.  After draining close relief valve and turn on water source when water flows out the hot water faucet turn it off and you should have enough air in the tank for expansion.  There is probably a procedure in the water tank manual for establishing the air head in the tank but the above instructions should do fine.

 

Tom

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Two possibilities:

  • Loss of air head, as Ron described.
  • The relief valve itself might need replacing.

Both are covered in an article in the library. Click the Library button above, select Quick fixes, then click Water heater relief valve.
 

Smoky

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Guys, I will try your suggestions.  But why won't the heating shut off?  I thought the thermostat would shut down over 120 degrees?  I can hear the heater continue to boil until I turn off the electric and/or the gas.

Going outside now to try Ron's procedure.
 

Tom

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Smoky,

Opening the valve should be done after the water in the hot water tank has cooled down, as cautioned in the article I referred you to.
 

Ron

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When water is heated it expands and like any other fluid is not compressible. ?Without a sufficient air head to allow for expansion the pressure build to a point where the relief valve has to do its job and relieve the pressure. ?The possibility of your thermostat not working properly while possible ?is not very likely. ?With a unit as new as yours I would bet it is just an insufficient air head and the expanding water has no air head to take up the expansion.  The thermostat will probably shut off when it is at the proper temperature but a given amount of water will increase in volume as it is heated to 120F thus the need for an air head.

DO NOT OPEN RELIEF VALVE OR REMOVE DRAIN UNTIL YOU HAVE COOL WATER IN THE TANK
 

Smoky

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Ron:

I am well aware of the safety concerns about relief valves, so no need to shout!  ;D

I am going to run your procedure of course.  It is just interesting to me that I can still hear the furnace running when it is boiling over.  Also there is nothing at all in the manual about air head procedures, but a lot about limit temperatures.  I will keep you posted.

Anyone here on the forum have a Suburbane RV dual water heater?
 

Ron

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I would not want anybody reading this topic to get burned so the loud warning was not necessarily directed to you but to anybody Reading the topic that might have a similar problem. ;D ;D ;D

The water is probably not actually boiling over but being released due to pressure build up and the water Temp is probably not hot enough to cause the thermostat to turn off.

We never have this problem probably because we drain the water heater and flush out the buildup once or twice a year as a part of maintenance.  It is amazing how much crud is flushed out.
 

Smoky

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Point taken on the warning.  No one should miss that warning!

I am also wondering why the water coming out of the spigot is SCALDING hot when we have no cold turned on.  Is that normal? 

Later today we should know more.  Gas and electric are off, while we wait for cooler water.
 

Ron

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With the water heater gas and electric off you can turn the shore water on and a hot water faucet on and let the water run till cool then turn the shore water off and proceed with establishing a head of air.
 

Alaskansnowbirds

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Smoky,

One method I use to try and assure that there is an air head in the water heater is when ever I connect to city water I leave the filter and hose empty. Then the first thing I turn on is a hot water faucet so all the air that was in the filter and hose is forced into the water heater.

I agree with the others. Your problem is more than not pressure opening the pressure relief valve instead of temp. Those valves open on pressure or temperature.
 

Tom

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Then the first thing I turn on is a hot water faucet so all the air that was in the filter and hose is forced into the water heater.

I'll have to remember to do that Don, thanks.
 

John From Detroit

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Just a thought.... but first a question

Does it do this both on "internal" and "city" water?

If it only does it when hooked to "City" (park) water, then do you have a pressure regulator in the line

I noticed mine dripping the other day... Found out I'd forgot the regulator and park pressure was 60PSI
Installed regulator, no more drips
 

Lou Schneider

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The water heater boils over because the RV water system is a closed system.  There are one way check valves at the water pump and city water inlets, so when the water expands in the heater there is no place for it to go until the pressure builds up and trips the overtemp/overpressure valve.  A stick house doesn't have a check valve at it's city water inlet, so water expanding in the hot water tank can bleed backwards into the supply line and pressure doesn't build up.

You can make an air bubble in the top of the hot water heater, and after a while it will go away again as the air is absorbed into the water.  A permanent fix is to install an accumulator tank anywhere in the RV's COLD water line.  This will provide the needed room to let the water expand and will also make the water pump cycle on and off less frequently.
 

Smoky

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Well after following Ron's instructions, we have stopped the leaking.  However, we still have erratic heat level performance.  Yesterday the water was only lukewarm and ran out quickly.  This after having all night to come to temperature.

Today is was so scalding hot vapor rose from the faucet.  LP performance appears more stable than electric.

Now that the air head has stopped the overflow, is there a troubleshooting check that can be done on the thermostat?  I assume the thermostat has some sort of limit mode that turns heat on at a low level and heat off at a high level?
 

Smoky

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Well creating a new air head only worked for 3 days.  Now it is boiling over again and coming out the relief valve as before.  I did learn one new thing.  It works fine if I just use the lp option.  But when I turn electric on, it boils over.

Going to check and see if Suburban is at the Pomona (sp?) show.  I would think this could be user serviced if it is the thermostat.  But Suburban will not help users over the phone.
 

Ron

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If it is just happening with the electric heater on it could very well be the thermostat for the electric heater.  If that is the case it won't be long till the air head Will be dissipated and it wil start doing it on the LP unless you cease using the electric heater till fixed.
 

Tom

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Smoky,

You did say "Initially this occurred when heating by electric, but now it does this with either electric or gas option" in your original message, but I missed the significance of electric misbehaving first. Good idea to have Suburban look at it at the rally.
 
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