I read the manual but figured I would try this site for better advice
7 years old
6 Flashes System Lockout.
1. Reversed polarity in 115 volt power supply.
2. Heater/burner not properly earth grounded, check pin
3 on wire harness plug (valve end) to burner
4 trials for ignition failed or 4 loses of flame tube for 115 volts, check ground path to burner.
occurred before set-point was reached.
3. Ground fault interruption (GFI) breaker causing
intermittent operation, try non-GFI outlet.
After 1 hour "soft" lockout, SmartValve control
4. Flame sense rod dirty or incorrectly positioned.
will initiate a new ignition sequence if the call
5. Vent system length exceeded, too many elbows,
for heat is still present. (SmartValve can cycle blocked exhaust/intake switch opens after light off.
this way indefinitely.)
6. Flame sense/HSI wiring condition/connections.
7. Low or no supply gas pressure.
8. Fluorescent lighting on same breaker as heater.
9. Damaged, defective, or incorrectly positioned HSI.