Water pump is surging-What's next?

The original SHURflo water pump in our 2002 RoadTrek 200 Popular was so noisy and would cycle on and off at any but full flow. It caused the PEX pipes to rattle. One night in Yellowstone, a neighbor tenter asked me to not try to start the generator at night. I did not have a generator. That was us taking a shower. I put in a Flo-Jet variable speed pump and it was wonderful. The water flow was just like we were connected to city water. The 2009 Itasca Navion had essentially the same pump and very similar problem. I elected to put in a SHURflo variable speed pump. Much improvement, but not as quiet and smooth flow as was our experience with the Flo-Jet, but swaping out the pump was easy. I will say this; If I were to do that again, I would install a relay at the pump and a heavy gauge wire back to the panel. The voltage drop caused by the reletively small gauge and the remote on/off pump switches would make the pump not work properly at times when only on battery power. The replacement pump failed after about a year (bearings) and SHURflo sent me a new one without hesitation. Worked OK from then on. I anticipated having to upgrade the pump when we ordered the 2018 Winnebago Navion 24G, but while it is not perfectly quiet and does cycle to some degree, I don't think it merits replacement. I believe the pump is a new design (4008 Revolution) with a by-pass feature that reduces rapid cycling and an accumulator tank is not recommended. On the 24G floor plan, the Truma tankless water heater and Thetford Tecma toilet are standard. A good pump is essential so that those features function problerly. Since the original pump is working out fine, I have not looked into the current offerings for replacements. From experience I have learned, the only way you are going to be happy with the results of an upgrade, don't go cheap. Get the best pump you can.
A quick search just now: I would go with Flojet V-Flo Constant Flow Water Pressure Pump if I had to replace mine. Pretty expensive, but if this pump is anything like the Flo-Jet we had before, it would be worth it. A couple of years ago when I was helping a friend with his pump problems on his fifth-wheel, I looked into some options. After reading the reviews on brands other than SHURflo or Flo-Jet, I think sticking to those would be a good bet.

Flarpswitch wrote:
Assuming that the pump and it's control is not the issue, I would look to the possiblility that there is air in the system on the pressure side of the pump. I had air in one branch that would make the pump surge until I opened the faucet to let the air out. I always replaced the pump that came with the RV with a variable speed pump that made the flow more even and quiet as well. The stock pump was extremely noisy and cycled on and off rapidly. The pump that came with our 2018 RV is a regular pump, but for whatever reason, the new design is so much better than in the past. I did have a surging episode when air got pulled into a hot water line to the shower. It caused not only the change in flow, but it made the tankless hot water heater crazy because it senses flow and then turns on.

What kind of pump did you prefer, and what do you now have?

Flarpswitch wrote:
The pump that came with our 2018 RV is a regular pump, but for whatever reason, the new design is so much better than in the past. I did have a surging episode when air got pulled into a hot water line to the shower. It caused not only the change in flow, but it made the tankless hot water heater crazy because it senses flow and then turns on.

Your new RV has a better pump because the manufacturer has no choice. A cheap, barely adequate pump will make your tankless WH really crazy.

SoundGuy wrote:

teeznu wrote:
Please share your thoughts.

SoundGuy wrote:
A city water check valve that's not sealing properly (a common problem) can leak air into the system after the pump, causing the pump to run when it shouldn't or surge when it does run. Capping that city water inlet with a threaded plug will establish whether this is your issue, or not.

Hurricaner wrote:
If the city check valve is leaking you will leak water not air as it is on the pump discharge.

You would think, but that's not always the case. If the pump has been off for awhile and pressure is relieved in the system air will leak into it past that city water check valve. I've experienced this myself and is why I always keep that city water inlet sealed with a threaded male plug.

That could happen if the internal check valve in the pump is also leaking but if it is not the air would not be able to get to the pump suction. Sorry for all the quotes.
Sam

teeznu wrote:
Please share your thoughts.

SoundGuy wrote:
A city water check valve that's not sealing properly (a common problem) can leak air into the system after the pump, causing the pump to run when it shouldn't or surge when it does run. Capping that city water inlet with a threaded plug will establish whether this is your issue, or not.

Hurricaner wrote:
If the city check valve is leaking you will leak water not air as it is on the pump discharge.

You would think, but that's not always the case. If the pump has been off for awhile and pressure is relieved in the system air will leak into it past that city water check valve. I've experienced this myself and is why I always keep that city water inlet sealed with a threaded male plug.

SoundGuy wrote:

teeznu wrote:
Please share your thoughts.

A city water check valve that's not sealing properly (a common problem) can leak air into the system after the pump, causing the pump to run when it shouldn't or surge when it does run. Capping that city water inlet with a threaded plug will establish whether this is your issue, or not.

If the city check valve is leaking you will leak water not air as it is on the pump discharge. Air in the suction is always a problem, if you have a fill valve, turn that on and let the pump circulate for a minute or so. My pump seems to always get air in it after a tank fill.

Sam

teeznu wrote:
Please share your thoughts.

A city water check valve that's not sealing properly (a common problem) can leak air into the system after the pump, causing the pump to run when it shouldn't or surge when it does run. Capping that city water inlet with a threaded plug will establish whether this is your issue, or not.

Only time that ever happened to me was when I'd forget to turn off the outside shower valves. The valve at the head would be off, but the main shutoff valves would still be on.

The same thing can happen if you forget and leave the inside shower head that way.

The other way it happens is when you still have the shore water hose connected but the spigot turned off AND your main one way valve is stuck open.

None of these three ways that cause surging will show any evidence...there won't be any puddles under the areas in question.

Agreed. Usually a leak in a line somewhere, causing the pump to cycle on/off or "surge". Or, it could be the filter screen needs cleaning.

Clean the filter. Could be air in the system but probably not.