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Your floor tile failure was caused by the following factors.
Individually they could have caused failure, but combined it was a certainty.
Chipboard floor - can be tiled onto but only with very special adhesives and with 100% coverage to tile and floor.
Heated floor - can be tiled easily enough but must have an uncoupling membrane such as Schluter Ditra, to separate the https://www.tilersforums.com/forums/tile-adhesive/ bed and tiles from the expansion/contraction stresses caused by the heating - as seen readily in the https://www.tilersforums.com/forums/tile-adhesive/ cracks in your photos.
PVA - simply put, this forms a skin and prevents (not aids) adhesion.
Acrylic primers, or SBR only should be used.
C2 https://www.tilersforums.com/forums/tile-adhesive/ has polymer added to bond to porcelain (standard sand and cement won't bond) but does not have anywhere near enough polymer to increase the flexibility required for a heated, timber floor.
Timber Floor - if your floor is "floating" as I suspect it is, then 90% of professional tilers will just walk away from them. There is just too much risk of movement, both deflection (bounce) and lateral (sideways) movement. They can be tiled. but not without a lot of prep, careful checking and special materials.
Tiles aren't back-buttered. - It is recommended that large format tiles, particularly with waffle backs, are back-buttered with a thin layer of https://www.tilersforums.com/forums/tile-adhesive/ to aid "bedding in" and ensuring a solid, even bond. It also removes any risk from tiles with dusty backs.
Hope that helps explain what has gone wrong!
Individually they could have caused failure, but combined it was a certainty.
Chipboard floor - can be tiled onto but only with very special adhesives and with 100% coverage to tile and floor.
Heated floor - can be tiled easily enough but must have an uncoupling membrane such as Schluter Ditra, to separate the https://www.tilersforums.com/forums/tile-adhesive/ bed and tiles from the expansion/contraction stresses caused by the heating - as seen readily in the https://www.tilersforums.com/forums/tile-adhesive/ cracks in your photos.
PVA - simply put, this forms a skin and prevents (not aids) adhesion.
Acrylic primers, or SBR only should be used.
C2 https://www.tilersforums.com/forums/tile-adhesive/ has polymer added to bond to porcelain (standard sand and cement won't bond) but does not have anywhere near enough polymer to increase the flexibility required for a heated, timber floor.
Timber Floor - if your floor is "floating" as I suspect it is, then 90% of professional tilers will just walk away from them. There is just too much risk of movement, both deflection (bounce) and lateral (sideways) movement. They can be tiled. but not without a lot of prep, careful checking and special materials.
Tiles aren't back-buttered. - It is recommended that large format tiles, particularly with waffle backs, are back-buttered with a thin layer of https://www.tilersforums.com/forums/tile-adhesive/ to aid "bedding in" and ensuring a solid, even bond. It also removes any risk from tiles with dusty backs.
Hope that helps explain what has gone wrong!