If your Aqua Hot burner isn’t firing up or smoking excessively on shutdown this could be your cure. Two possible failure Scenarios- The fuel solenoid seats tend to wear down allowing excessive fuel to pass during purge cycle or If you have a no fire situation it could mean that your solenoid has failed not allowing fuel through. Whether you are replacing just the seat and spring kit or replacing the whole fuel solenoid this video will help with your repair.