You'll have to prove that popes burned heretics in the eighth century, first. Got any documentation you can share? You'll also have to point out theological errors of the popes. After all, that's where their infallibility lies. There's a large period of time, though between the eighth century and Luther.What false teachings?
I have a friend who recently, just weeks ago passed away. Br Pascal H. He informed me speaking with probably a sense of revision and in the context of the brothers academic learning that the Popes became too political in the eight and ninth centuries. I suspect this may be because they had so much political power and because of the Islamic forces.
I am not sure when death began to be enforced upon the ones the Pope found heretical. But a Pope of such a hard heart, I would say was under the doctrines of demons and I would not trust his teachings. While the Ex Cathedra teachings were treated more carefully.
The false teaching I refer to are the ones coming from hard hearted ones and bitter ones. Rivalry between Protestants and "Papists". It still lingers in Northern Ireland. Teachings against spiritual gifts persisting after the death the the last apostle. The witch hunt concepts. Punishing the ones of erring ways instead of blessing them. Our justice systems is full of old Christian world ideas. It very much differs from the justice of the apostles and from recent times missionaries, who converted head hunters rather than try to imprison them...
Teachers who go to extremes are dangerous. When Satan can't block in front, he gets behind to push us too far. Not too much love, or worship, but too much force, strictness, opulence, ambition, control... things on the periphery of Peter the apostle's mission.
Other false teaching lot off all so called "prosperity Gospel" teaching as evil, and again create a sense of rivalry, and want to force silence rivals unless they "recant"...
They lost the teachings on the presence and power of Jesus' precious blood.
They don't ask for "more Lord."
There is the matter of sinful priests who confessed their sins, but were able to keep their positions or merely be moved to new parishes. They were not sent out of the priesthood at first signs.
These priests, are not generally recognized as repentant by the public despite confessing. They are useless as preachers. No one wants to touch them. Whereas there are stories of confessors who repented and this moved people. Like Nicky Cruz or Jan Erickson. So there is false teaching in the confession tradition.
Repentance and becoming above reproach and the goodness of Jesus to such a one and those they serve is salt. If he returns to sins the salt loses it's flavour. The testimony flavours and preserves Christian society. Salt and light are mentioned together in Jesus' Gospel. Light should be on a high place, sermons. It is not good enough to be sorry for the same sins each week, so if there is a bogged in sin, one needs a break through, to overcome.
I personally can't believe in transubstantiation and the ordination of priests continuing by the laying on of hands until now.
I find communion a valuable relic of the old church. It keeps people seeking to be completely sinless. But we miss the love feasts and the living water, healing, sprinkling of Jesus' blood, the fire of God, the anointing oil, as for Timothy and the prophets, and eating the bread of life outside the mass. These powers help us to be clean and become holy characters equipped to serve others. But thankfully they begin to be found again in the Catholic Charismatic Renewal.