Water mystery on pump mode

DownTheAvenue wrote:

georgelesley wrote:
Once while camping we had the same thing happen. Late at nite with no other ideas, I took the air fitting I use for blowing the lines to winterize the system and screwed it in the fitting, that stopped the problem until I could put in a new fresh water fitting.

That is typically what causes the back flow preventer to fail- air pressure. Using an air compressor to blow water out of the pipes often is down at a volume or pressure greater than that valve is designed to handle, and, presto, failure.

I suspect that is why ours failed since the first time I blew the lines I forgot to initially reduce the air pressure. That is something i always do now. However when I changed the city water fill I discovered it was 1/4 turn loose which explained the slow mystery leak we had that i had chased for a year. Since a new city water assembly cost somewhere less than $20 I just changed it all rather than messing with the check valve.