On Board Water Pump Question?

To bring closure to this thread, I may have found the solution.

It was not low-point drains, as I thought. They are bone dry. But when checking again, there was water standing behind the outside panel where the water heater is. I dried up the excess and wait and sure enough, it eventually got wet again.

It is not the pressure relief valve, it's the anode rod, drain hole. I normally drain the water from my heater after every trip, and never over tighten when replacing the plug. This would account why sometimes the pump comes on more than others, the anode rod is sealed tighter sometimes, and sometimes not. As said, I never over tighten, and I never use any kind of thread sealer, like Teflon tape.

So, considering we're sleeping in the camper every night at home and using water in the camper and the water heater is on, I loosed the anode rod and simply retightened it again, reseating it. Well, I waited for the pump to kick on again. As far as I know, we went all night and it never pulsated again.

Been in the camper every night since, and the outside water heater compartment is dry, and have not heard the pump pulsate any more.

I think, maybe the water escaping from the water heater via the anode rod drain hole is so hot, it sometimes evaporates. When I looked in the past, I missed it, poof! evaporated! This time, I must have hit it just right to catch the water standing there.

This would also explain why sometimes it acts up more than others, considering I drain the tank when we're not using it.

I think my mystery is solved. We're heading out for another State Park (actually in about 10 minutes), and am not draining the tank. It will be interesting after bouncing down the road and setting up tonight again if it pulsates again. We'll see.

But I do think this is the source of my problem. I'm about 90% sure. I just need to test it out now a bit better.

Next time I drain the tank, I'll replace the anode rod with that Teflon tape and see if that prevents any drips!

Thanks everyone one... actually, it was the low point drain investigation that led me to this conclusion. Thanks for the suggestion! It led me to the right path.

Along the same lines, not trying to Jack the thread, on our camper, noticed this trip after long hours on the road, every time seemed to be some air in the line going to the bath. First turn of the pump after all day on the freeway would result in some water hammer in the lines until I'd run the toilet and bath sink for a min. No leaks. Kind of like first fill after blowing out the lines for winter.
Maybe something pull a small vacuum and cause air in the line?

All seem like good potential diagnoses. One more to consider. U said the water heater was extremely hot and it doesn't happen cold. IMO that may eliminates the city water check or pump check or seals. Is it cranked up too hot and evaporating a little water. Build a little vapor pocket, pressure drop, pump kicks for a second?

I'm going to go along with the air cushion and slight leak in the check valve. I had the same problem and rather than go thru the hassle of R&R the pump and replace or clean the internal check valve I bought a Shurflo check valve with 1/2" barbed hose fitting on both ends. No more burp. Cost about the same for the two valves, about $15 for the add on valve.

If the pump cycles for a "split second" that tells me there is no air cushion in the water heater. The fact that it cycles at all, probably means a slow leak of the pump check valve.

It is clear to me that your pump is backflowing a little bit. Seeping back through the check valve.

Question is do you need to do anything. The pump is doing its job, which is to keep the system pressurized. If it cycles a few times per hour to do that job, it isn't really hurting anything. Depends on how annoying you find it to be.

Pretty easy to fix, and it will get worse. But not really an emergency, and most importantly, does not necessarily mean you have a leak.

AJR wrote:
If I turn on the water heater the pump does as the OP describes. I found the over pressure valve dribbling so slow the water was vaporizing below the valve. As so the hot water is too hot. Have not looked into how to turn down the temperature yet.

If you have a Atwood the normal temp t-stat is 140*F.....if it fails to stop heating process the ECO (high temp) shuts down heating at 180*F
IF the ECO opens you would get a 'Fault Light' (Red light on panel) and no more heating until YOU reset fault

If you have a Suburban the normal and high temp t-sat function same as Atwood except YOU would have to manually reset the High Temp t-stat


So your water heater is probably functioning correctly ----140*F water is HOT but that is how they extend the hot water use.

Course if you have an Atwood XT model.....normal t-stat is 160*F
Everything else same. Mixing valve controls hot water to system at 130*F

DutchmenSport wrote:

Old-Biscuit wrote:
You have a very small leak......small leak at a fitting on low point drain line...

Good observation. The low point drains are the one thing I've not considered. Still, if it was a leak, why does the pump cycle "only" when the water heater is on and water is hot. When cold, it doesn't do this. I would think the pressure would be the same with hot or cold water in the tank? Also, I've not noticed any loss of fresh water in the fresh water tank. Still, I'll check those low point drains. I am a firm believer in taking the least evasive action first. This one is simple to check. This does make sense, I have checked every nook and cranney. I've not found any leaks inside, no drips under the trailer, and no wet spots on the floor, or anywhere, except the low point??? Never thought of that. Still, only when water heater is hot... still puzzled. .. Thanks.

We're doing too much camping right now to mess with the water pump itself for that check valve. Once camping season slows down I'll check that out. I don't want to end up screwing something up and then have the camper out of commission while I figure out how to fix something I messed up. If the low point isn't the problem, check-valve is next.

Thanks again.

Water 'swells' when heated
Swell can increase pressure enough to weep from T&P, drip from hot low point or even push back thru pump
Doesn't take large quantity to drop pressure so one would not notice a change in fresh water tank level.

And adjusting pump pressure would just change 'where' it would cycle vs fixing the reason for cycling

It might be the TPR valve on the water heater

As the water heats, it expands, pressure increases and the TPR drips a bit to release that excess pressure.

Then the water cools a bit, and the pump kicks in cause now the pressure is down a bit.

Possible solution.

Drain and flush the water hater, re-establishing the full air cusion

Solution 2, New TPR

Solution 3: reduce pressure on pump if it is adjustable, Just a couple of PSI.

If I turn on the water heater the pump does as the OP describes. I found the over pressure valve dribbling so slow the water was vaporizing below the valve. As so the hot water is too hot. Have not looked into how to turn down the temperature yet.