We have Model 21VP40E-1PA gas hot water heater and have talked to Rheem about the problem;but no help yet. It heats the water fine but the pilot keeps coming on over and over again. It clicks twice and the pilot relights. I still have hot water though. I bypassed the clear plastic tubing which they suggested but nothing changed.
I am not all that familiar with the model you have stated but the description of the problem you are having was the same I had with what I beleive is a similar model to yours, after a whole lot of mucking about trying to identify the fault it turned out to be a combination of two things – one being a faulty pressure switch from the fan to the controller switch and the other was the circuit board. Rheem should be able to send you or your service person a manual on the fault finding tips to follow for this model.
Selgas Services Ltd Craftsman Gasfitters, Plumbers, Electrical Service Technicians