Your check valve broke, that's why the spring came out. If you have possession of the spring - great. Had the spring gotten into the hot water heater, it could have come in contact with the heating element and shorted it out. You should have two check valves; one for cold water in, and one for hot water out. Replace them both and make sure the arrow (on the check valve) points in proper direction for water flow. Make sure you turn off hot water circuit breaker prior to starting job.
I only saw one on the cold side coming in. The spring is still inside the little white plunger/plug fell out. Unless they installed the valve further away from the hot water heater but if it's not pretty close to water heater what would be the point ?
I gutted the check valve on the outgoing line years ago when it was giving me constant problems, even after installing a new one. It works fine without it. The only problem is if you want to winterize using antifreeze, it will backflow into the water heater tank.
Paul (KE5LXU) ...was fulltimin', now parttimin'
'03 Winnebago UA 40e / '17 Jeep Grand Cherokee toad
Winnebago uses two check valves. One on the input and one on the output. The one on the output allows a single diverter valve to bypass the heater for winterization.
A tech at the Winnebago factory told me that the one on the input keeps the pressure increase as the water heats up from pushing hot water into the cold water line. It appears that a lot of builders don't use that one.
Clay WA5NMR - Ex Snowbird - 1 year, Ex Full timer for 11 years - 2004 Winnebago Sightseer 35N Workhorse chassis. Honda Accord toad.
I recently had an over-pressure problem due to hot water heating. In the course of diagnosing the problem, I replumbed the lines from an outlet (hot water) check valve and a three-way valve to no check valves at all and three individual valves (cold in, hot out, bypass). This is simpler for most of us to understand, and less failure-prone.
2008 Holiday Rambler Admiral 30PDD (Ford F-53 chassis)
2009 Honda Fit Sport