water pump

We just purchased an 07 Salem made  by Forest River.  With our other campers we have only been hooked to city water. Now we have a lake lot and must use the fresh water tank and water pump.  When we are trying to use the hot water  the pump comes on but the water cycles from hot to cold.  What is the cause for this.  I don't think it would be a very nice shower like that!

Hard to say.  Do you mean that it continuously surges from hot to cold to hot again?  Or do you mean it starts hot and quickly goes cold and stays cold? 

When you say "cycles from hot to cold", I'm guessing you mean every few seconds, right? One possible reason is this: When you are hooked up to city water, the pressure remains fairly constant. When using the pump, the pressure drops to a preset level, then cycles on to build it back up. This repeats as required. Due to the cold and hot water pipes being routed differently (the path through the water heater is probably much longer), the water pressure may be building faster for the cold water than for the hot. Your shower head should have a valve of sorts that shuts down, but does not completely turn off, the water while you're lathering up, and helps maintain both the pressure and the hot/cold mix temperature. If you don't already do so, try doing this and see if it helps: Turn on the water and adjust for the right temp. Get wet and shut of the water at the head (it will still dribble slowly). Lather up a portion of your body. Turn the shower head back on to rinse. Turn back off, and repeat as necessary. This is how most of us do it without any hot/cold problems.

Another possible problem is that you have lost the 'head' in the water heater. That is the quantity of air that is retained in the water heater tank, but after a period of time, it gets absorbed into the water. Try this: Shut off the water pump, open the water heater access door outside and locate the tank drain plug. Remove it, and water will start to drain out. Now operate the lever on the temperature/pressure safety relief valve near the top. Water will start flowing out the drain hole faster, and air will be sucked inside. Drain about 1 gallon total. Release the lever and replace the drain plug. Don't forget to use new Teflon tape on the threads.

If you still have problems, get back to us and we'll try to see what else it could be. Good luck!

Karl said:

.....locate the tank drain plug. Remove it, and water will start to drain out. Now operate the lever on the temperature/pressure safety relief valve near the top.

Click to expand...

Don't try that when the water is hot though.

Tom,
Good catch - back at you! Thanks!

It purges back and forth between hot and cold.  We may have let out the "head in the water heater ourselves.  The first time we used it, we couldn't tell if it was full  of water or not--new rv.  So we pushed the valve to see if there was water in it before turning on the element.  Good thing because the dealership had all the lines going in and out of the water heater shut and it wasn't even plugged in. So, maybe we let the air escape by messing with the valve.  The other thing is that we can't get the drain plug off.  We never had this problem with our other two travel trailers--guess we'll have to keep trying.

thanks for your help

Cycling from hot to cold and back is almost always caused by having some cross-over valve open in the water lines, which allows cold and hot to mix in the lines themselves. There are three places in an RV where this commonly occurs:

(1) an outside shower or rinse head is turned on at the faucet but off at the head. Water flows between the hot and cold sides and through the lines to  another faucet.  Fix: Close the faucets at the outside shower.

(2) Same as (1) but at the inside shower head. Fix: Same as above

(3) Water heater bypass valves are partially open or closed, i.e. not fully in the heater position. This lets water cross over from a hot line to a cold line, resulting in the cycling at any faucet. Fix: Put the water heater bypass valve fully in one position of the other.

I suspect (3), since you said the water heater valves were not set correctly and you or the dealer have tinkered with them since.

Sometimes problems show up on the pump that did not appear on city water, becasue the pressures are different and also less constant when the pump in in use.