The design presented here will only work with heaters that use a "blue wire interface".
Of course the colour of the wire is only that of a PVC sheath.
The important aspect is what the electronics hardware exists at either end of the blue wire.

If your heater uses one of the following style controllers, this design will be compatible:

The digital protocol controllers use one of 2 styles of loom connection.
A 3 pin triangular waterproof conenctor, or a smaller round 3 pin waterproof connector:

The all important part though is the control PCB within the heater.
This is the PCB within a blue wire enabled heater that will 100% work with this controller design.
The blue wire interface is circled in the following photo:

The important selection criteria is whether a dual transistor multiplexer is evident on the input path of the blue wire, this sort of topology must exist, if the wire runs direct to the microprocessor, it is most likely incompatible, and probably an analogue voltage from a pot:

This heater PCB is DEFINITELY NOT COMPATIBLE
The buzzer is the first giveaway, plus the lack of a main relay. The controller will also just be a basic pot and switches.

This sort of controller has the right plug, but wrong protocol - it cannot be replaced with an Afterburner.!

Required Arduino Libraries

JSON dictionary

Bootloading production PCBs

Hardware design files