I have the S.30 error message how can I fix this issue and what is this issue.
The S30 status code on the EcoMAX 635 is a signal telling you that there is no heating demand from external controls. This typically means that there is no problem as it is not an error code. The room thermostat measures the room temperature against the desired set point inputted into the controller. If the room temperature is lower than the set point then the stat calls for heat from the boiler. If the room is equal to or greater than the set point then you should see the S.30 status code.
Basically there is no problem with your boiler.