Originally Posted by SHOCKWAVEJON
I didn't see a bypass on our water heater so don't think it has one. I tried letting the pump run for several minutes, and even held open the pressure valve on the hot water heater to release air pressure and it still continued to do it.
Your bypass (you should have one) may not look like a 3 valve setup; it may only have one valve and a stand pipe (see photo).
However a pulsing water pump is normally caused by a slow pressure leak.
Causes I have found for slow leaks are:
1) Leak at water pump outlet fitting (or "whole camper" water filter). Leaks at pump inlet will cause a failure to prime; not cycle.
2) Check valve to fresh water tank. This valve (spoken of as one check valve, there are actually 3, one for each sub-pump in the pump head assembly) is IN the pump head. Draining the hot water heater through the low point drains during winterizing is the usual suspect. A bit of anode or calcium can prevent complete closure and cause a slow bleed back to fill your fresh water tank till it overflows. (check the FW tank for an increase in level.) Cure: rebuild or replace pump.
3) Faucet valve not fully seated (same cause most times). May need to remove valve body and flush out crud.
4) Toilet valve slow leak (same cause) will fill bowl to overflowing. Cure: Flush out system and replace/repair toilet valve.
5) Pump pressure switch malfunction (normally the pump will not shut off; not cycle). Cure: rebuild or replace pump.
6) City Water Check Valve failure. Look outside at the city water hose connection and look for water running down side. (you will need to disconnect the city water hose to check if connected).
ALL leaks must be located and repaired. A leak undetected can destroy your camper pretty quickly.
Hope this helps.