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What is the age of the house in question?
If this has been going on for some time with excessive heat over the past 2 weeks I doubt the absence of a DPM would cause significant issues, since the argument would be moisture from the ground is rising, but with the water table very low at the moment and the ground bone try I cant see an argument being made.
Depending on the age of the property I would check you have a DPM on the external brick work often can see small parts sticking out of the mortar, and good chance if there is one on the brick work there will be on the subfloor, I would also check who signed off the building as this would have been checked as part of building control.
I would argue its for the insurer to prove the absence of a DPM (since if the building is traditional type and signed of by Building Control, and evidence of one on the brick work its highly unlikely one isnt present on the subfloor, especially if its not become an issue until recently).
Are the tiles linoleum, if so the thermal properties of those are minimal, but it may be another underlay, levelling compound or similar was placed under them which is insulating the floor.
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