Hot water overflow

[Tom]

This question relates to our boat, but it could just as well apply to the coach, since both use a similar hot water system (the HW tank on the boat is larger)....

If I leave the hot water heater on, eventually I hear the water pumps cycle on and off. I also see water coming out the side of the boat. If I ignore it or, like last night/this morning, I don't catch it, It will eventually empty the fresh water tank. My temporary "fix" is to heat the water and turn off the water heater. This problem started about a year ago, and didn't exist prior to that. What I'm suspecting is that there's a heat or pressure operated safety valve that's malfunctioning &/or the thermostat isn't working. Anyone seen this problem?

 

[Ron]

Could very well be the pressure relief valve on the HWT.  If you can get to the HWT you should be able to see the brass pressure refief valve. Somtimes just pulling the lever to manually operate the valve will allow debris to wash out from the valve seat area.  If that doen't work replace the valve.

 

[Steve CDN]

Tom,

In addition to Ned's suggestion about activating the lever on the pressure control valve, I regularly flush the HWT using a contraption I made that attaches to a garden hose, but is curved 90 degrees on the end.  It is surprising the amount of deposit I flush out of the tank every three or four months.

When I flush the tank, I replace the inexpensive plastic drain plug (75 ? )as the head can easily shear off from the torque stress when tightening more than once or twice.

 

[Tom]

Thanks Ron. It's easy to get at; Lots of romm below decks. I'll press the lever in the morning.

 

[Tom]

Do you by any chance have a photo of the contraption Steve?

 

[Ron]

I have a device I bought at camping world that I use to flush the water tank.  Can take a photo tomorrow and post it.

 

[Tom]

OK thanks Ron.

 

[Steve CDN]

I don't have a photo with me, but when we return to the coach in a couple of days, I'll take a picture.  It originally was a device for flushing an outboard motor, which I sawed in half, sealed the open end with epoxy.  It's already made to be attached to a garden hose and is made with a 90 degree end where the water comes out.  Cost me nothing since I got it in a junk box from someone who was getting rid of it.

 

[Tom]

You mean half a pair of fushing ears like these?

 

[Steve CDN]

You mean half a pair of fushing ears like these?

Yes, exactly.  Now those cups have to be discarded and the cups are attached to a 90 degree fitting which can be extended for better fit into the tank drain opening for flushing.

Thanks for the photo link!

 

[Tom]

I'm still having a tough time visualizing it Steve. Maybe I shoul wait for your photo 

 

[Gary RV_Wizard]

Just about any small nozzle that you can stick in that little tank drain hole will help flush the silt out of the tank.  A lot of it can accumulate in a short time, depending of course on the salts in the water you use.  However, I don't see how silt could cause your overflow problem - that's got to be either the relief valve or a crack in the tank.  The relief valve could be opening early or just have a bad seal (usually neoprene), but it is also possible the tank actually is overheating and the relief is "working as designed".  ???

Another thing that will sometimes cause a relief valve to "weep" is lack of an adequate air "head" in the heater tank. There should be a cushion of air at the top. Assuming the relief valve is in the side of the tank a little below the top, the technique is to open the relief and let water drain until it stops, i.e.the water is just below the level of the relief. That assures there is an air cushion.  However, if the relief valve seal leaks, the air cushion will disappear over time and you will have to repeat the process (or replace the valve).

 

[Tom]

it is also possible the tank actually is overheating and the relief is "working as designed".

That was my first choice Gary. When I get out of my PJs I'll go down below and check it out.

 

[Dolphin Jockey]

Hi Folks,

FWIW, I'm not a fan of using the PTR valve to put an airhead in the water heater.  Years ago I read somewhere that it's an invitation to problems with deposits clogging the PTR valve and affecting its proper operation.

There's another way to place an airhead in the water heater: pump it in through the water hose between the RV and the campsite hookup.  Before connecting the water hose to the RV ensure it is drained completely.  Turn on any hot water faucet at a sink in the RV.  Now connect the outside water hose to the RV and turn on the outside spigot.  As water flows into the RV it will force air ahead of it into the water heater.  Once the proper airhead is established any excess air will flow out through the open hot water faucet.  Allow the air+water to flow until there no longer are air bubbles coming out,  You now have a proper airhead without messing with the PTR valve.

 

[Tom]

Thanks for posting that information George. A couple of questions/clarifications:

• I assume you're saying to hook up to the "city water" inlet vs using the gravity feed (?)
• Why doesn't the air get pushed out of the open facuet?

 

[Ned]

After draining and flushing my HWH, I leave it empty and when I turn the water back on, the air in the tank creates the airhead.

Tom, the water enters a hot water tank at the top and leaves from the bottom, so as soon as the exit is covered with water, the remaining air forms the airhead.  The result is much the same as my method.

 

[Tom]

the water enters a hot water tank at the top and leaves from the bottom

Thanks Ned, but color me confused.  ???  It's been many years since I worked on domestic hot water heaters for a living, but they always used to have cold water coming in the bottom and hot water out the top. Any reason that RVs would be different?

 

[Ron]

If I recall correctly  the cold water should enter near or at the bottom and hot goes out near the top.  If the cold was to enter the top the cold water would cycle to the bottom cooling the heated water and the water heater would be very inefficient.

 

[Dolphin Jockey]

I assume you're saying to hook up to the "city water" inlet vs using the gravity feed (?)

That's correct.  Let the city water pressure force air from the empty hose into the RV ahead of the water.  By having a hot water faucet on before the city water is turned on the air will be forced to flow into the water heater.

I've read the other posts addressing air coming out the hot water faucet and I agree with Ron.  On my Suburban water heater cold water enters at the bottom of the tank.  Hot water comes out NEAR the top of the tank, not AT it.    If air is pushed in at the bottom of the tank it will rise to the very top.  As long as the water level is BELOW the hot water outlet air will escape via the open hot water faucet.  Once the water level rises TO the outlet you get a combination of water and air out of the faucet  Force more water in the bottom and the air at the top will start to compress, allowing the water to rise slightly above the hot water outlet.  Once that happens you no longer have air coming out of the faucet, even though air remains at the top of the tank.

That airhead is necessary because water expands when heated.  As it expands the airhead compresses.  That's why there's a sudden rush of water when you first open a hot water faucet after the water heater goes through a heating cycle.  If that airhead were not there then there would be considerable leakage of water out the PTR valve as the water is heated.

Hope this helps.

 

[Ron]

Excellent explanation George.  That is as I understand it'