This one is all so common to Munchkin boilers. It occurs after three failure attempts to light it.
It signals that there is a flame detection problem.
This can happen because of the following things:
- There is no gas in the system;
- The inlet and outlet pressure at the gas valve are not balanced properly;
- The flame rod is damaged or dirty;
- The unit is contaminated due to improper care;
- Check the duct system and make sure it is not blocked;
- Check the condensate line and clear it, if necessary.
If you do not have experience with such boilers, use professional help instead of trying to fix it yourself.