Shouldn't need a combination valve. They're pretty tough and they last darn near forever.
Here's what you're dealing with internally...
There are two tools you need if you've managed to make the combination valve confused or angry with you.
This tool pulls on the bleeder rod so that it opens the metering valve to the front brakes.
The differential pressure valve has to be centered when you're bleeding the system. Locking it down in the centered position helps immensely.
If the differential pressure valve is out of whack you can re-center it by opening bleeders on the opposite end of the vehicle from the direction it tripped and pushing the brake pedal down just til the BRAKE light goes out.
If you overdo it just close the open bleeders and open the ones that you left closed and push the pedal carefully down til the BRAKE lamp goes out.
Once the differential pressure valve is centered you unscrew the warning lamp switch from the combination valve and screw in the differential pressure valve tool like this cutaway shows.
Pressure pot bleeding is IMHO the best way to fully bleed the system when you have no assistants... and when you don't want to replace or re-build the master cylinder.
Why do I mention the master cylinder???
The pedal push method almost always pushes the old piston seals that are stiff, since they aren't in their first flush of youth, into an area of the master cylinder bore that's not worn, so it's smaller, and the stiff cups don't rebound to the diameter of the worn bore quickly if at all. That section of the bore can also have more than a little corrosion that'll sand the seals as they grind past it... That's why your master cylinder sometimes blows out soon after a brake line failure.