The SP2034D is listed as a direct replacement for the AP15256D.
We are not able to confirm the cause of your lack of hot water. We strongly encourage you to not attempt to trouble shoot gas equipment and have a licensed professional technician review your application and troubleshoot on-site to determine which part is causing the issue. The technician will be able to make recommendations in accordance with safety standards outlined by the Authority Having Jurisdiction in your local area, Replied on June 05, 2023 by Ori from Industrial Stores