I installed a water heater gravity circulation line but it does not circulate. On newer heaters I learned that there may be a flap that prevents siphoning. How do I remove this? Rheem Model # Prog50-42NRH67PV Manufactured 4/11/2016
I don't think it would be possible to have a device to prevent a typical thermo-siphon arrangement, as the circulation path is the same as the normal path that heated water takes from tank to point of use. If the arrangement is not set up properly then you might not get circulation (i.e. check valve at return line).
Picture stolen shamelessly from the internet.
Here is what to do; It works cause I have done it in previous homes. Looking at the picture posted as a guide, pipe as shown but add the following: You have to cool the water in the return thermosiphon line and increase that line to 3/4". To cool the water, add about 10 to 15 feet of hot water heating finned tubing (just the tubing, not the enclosure) and it can run horizontally. At the line just before it enters the hot water tank install a drain valve so you can start the flow of water through the thermosiphon line (run water until it comes out hot). You will also have to add the check valve as shown (3/4 inch swing check and not a spring loaded check). Or, this may be a better option for you. If you choose to add a pump and timer as I have done in my existing home, then you will not have to add the cooling tubing. Buy the smallest bronze of stainless steel pump you can. Iron pumps will not last pumping domestic water. The pump I used is a Bell & Gossett model NBF-8S/LW, 1/2" and draws 38 watts. I wired the pump through a cheap plug-in timer to run during the day only. I have almost instant hot water at all sinks and showers.