hot/cold water cycles only on shower

[coachcadet]

I have an older Coachman Cadet.  I had to put a new 6 gal Atwood water heater in it last year.  I have a trickle shower head installed.  I have almost always used the water pump to supply the water.  The water in the shower cycles from extreme cold to extreme hot.  It gets super hot when the pump comes on and then cold when it goes off.  I did not have a bypass valve on the old water heater and this problem never occurred.  The water temperature does not fluctuate on any other faucet.  The shower is hooked to the bathroom faucet via a "D" spud.  When using the faucet in the bathroom or kitchen there is no fluctuation in temperature.  I am thinking that I might need an accumulator tank but I am not certain that would solve the issue.  Any ideas/suggestions are greatly appreciated.

 

[007]

Welcome coachcadet to the rv forum.
Do you have a outside shower and are the two faucets turned off?  Do you have a mixing valve for the shower or you adjust by two faucets?
A tank may give a steadier flow but isn't necessary.

 

[Gary RV_Wizard]

This problem is caused by hot and cold water mixing somewhere in the system other than at the shower valve. Since you recently installed a bypass at the water heater, it is likely that is the culprit. Either it is installed wrong or the bypass is partially open, allowing cold water to bypass the heater and flood into the hot pipe as the pump cycles. The other common places where this happens is at an outside shower head, when the water is shut off at the head but the hot and cold valves remain open, allowing the two to mix at that point.

The problem typically shows at the shower only, probably because the shower has a higher flow rate than most faucets and besides, you notice the fluctuation a lot more when standing in the shower!

 

[coachcadet]

I should clarify that I don't have a bypass valve installed on the new water heater either.  There is not an outside faucet/shower.  I would notice this temperature change when just washing my hands if it were happeneing on another faucet.  The water goes to scalding (literally) hot.

As for the shower, I simply adjust it using the hot/cold handles on the bathroom faucet. 

 

[Gary RV_Wizard]

OK, I mistakenly thought you had installed a bypass with the new heater. Since the problem started with that new heater, something you did changed things.  Might you have gotten the heater inlet and outlet pipes reversed?  You would still get hot water some of the time but likely would give some unusual results. The inlet brings cold water in at the bottom of the tank and the outlet pulls hot from the top, so that you always get heated water as long as the tank has any (hot water rises). If reversed and you are sucking your 'hot' supply off the bottom, you would get colder water when the pump delivers cold to the tank and it settles down from the top..

 

[007]

Most tanks have a H for hot and C for cold on side of them.
If you reverse, what Gary described will happen.

 

[coachcadet]

Checked the hot/cold connections on the WH and everywhere else and everything is the way it is supposed to be. 

I am wondering if maybe I lost the "head" in the WH tank and that is what is causing this.  Is there a way to test for this?

I was going to try to test tonite on city water connection to see if the same happens, but with 2 little ones time just seems to fly by. 

I appreciate all the tips. 

 

[GKman]

I'm thinking that there is a loose part in the shower faucet that doesn't maintain the flow opening precisely.  When the pump starts the pressure pushes the hot valve open farther.  A loose washer in an old fashion faucet can do this.  Take a look in there.