Drastic water temperature change while on water pump

[Wolf8U]

Drastic water temperature change while on water pump. While boondocking, we took quick showers - very quick. While the water would run, when the pump came on the water was scalding hot! When the pump turned off the water was tank temperature! This would repeat every 10 - 15 seconds. Is there a solution for this, besides not taking showers? On shore water runs perfect no issues, just happens while on the water pump.

Any suggestions?

[javelin]

I see no responses to you so far so lets start the ball rolling. When on city water you say there are no problems so the issue is between fresh tank and high pressure pump line side feeding the hot water tank as a first WAG. Some clarifications though - what do you mean by:


“When the pump turned off the water was tank temperature! This would repeat every 10 - 15 seconds.”


When you are on pump water (from fresh tank), does the hot and cold water flow normally though other coach sink faucets, but just not at the bathroom shower ?

[Bob Denman]

One other question: Is your hot water system tankless?

[wrapped]

Make sure outside shower knobs are turned off not just the button on the shower head

[Wolf8U]

To start, outside shower is off, shower hose not even connected. The pump on/off is cycling. Hot and cold water throughout the coach. Outside kitchen is off, inside kitchen and sink in bathroom is off. When doing dishes or washing hands really don't notice water flutuation. We have a 6 gallon tank with electric and gas. Shower if you turn on the hot only it's hot. And if you turn on the cold, well it's tank temperature, cool, under bed. When both are on together, when the pump cycles on it is scalding hot, when the pump cycles off, it is tank temperature.

[javelin]

Another head scratcher here I think.

So, when on city water input only the hot and cold faucets in the coach all seem to work fine, which should also indicate that the water heater bypass valves are set OK (famous last words) and there is likely nothing wrong with the shower mixing valves either.
If I understand your description correctly, when on pump only and each shower tap is turned on individually, temps are normal and the pump does not cycle but stays running. But when both hot and cold taps are on in the shower you get the pump cycling on and off every 15 seconds or so. Is that on 15 seconds then off 15 seconds? When any other tap set in the coach has both hot and cold turned on together (when on pump only) do you have the same pump cycling and temp fluctuations result?
I don’t think the pump should cycle with any combination of shower water valves plus shower head being “fully” open/on. It should run continuously I would expect, except in situations where flow is very low (soaping up shower head is off, but trickling) and the high pressure side of the pump meets spec shut off pressure momentarily. Then resumes when the trickle drops pressure enough to re-start the pump. So why would the water pump shut off at all when only both shower valves and shower head are full open?
You could try removing the shower flex cable with shower head from mixing valves and see if anything changes related to this problem at the shower mixing valve output/pump cycling. If the shower mixer valves flow freely but the pump still cycles then maybe the pump pressure switch is acting up or perhaps the low pressure side of the pump is starved for water......check filter for obstructions and fresh tank for good flow/valve is open fully.

[16ACE27]

Check your water heater bypass is fully shut and the isolation valves are fully open. This is starting to be a common theme with these water temperature changes.

[Wolf8U]

We have not noticed any temp fluctuation from any other faucet, however they are never on long enough, will check that out tonight or tomorrow. I will also remove shower head as suggested to see if the fluctuation stops. Thinking back the pump stayed on with the bathroom faucet and the outside kitchen. Got to say I just don't recall the kitchen sink much, we do all our cooking and cleanup outside, the kitchen sink is mostly used as counter space, however i will give that a try as well.

Just in case I haven't mentioned this, thank you to everyone for your time with this issue.

[Wolf8U]

Well had to do fast winterization, prior to that, tried all the sinks the shower seems to be the only faucet that the water pump cycles on and off.. Forgot to take the head odd the shower to see if that made a difference, will need to wait until next year.

Thank you everyone, will let you know in March or April.