Damp around base of toilet - advice needed q

[Mac1291]

Hi guys, I have an issue with my toilet that I would appreciate some help with. We bought the house in November & noticed that the existing toilet had damp around the base of the toilet bowl, I assumed that like the rest of the house it had been neglected & we were getting a new suite anyway so I wasn’t overly worried. I removed the old bath suite over Christmas & then the room had a plaster. Whilst the bathroom had no suite during this time there was still a damp mark on the floor but it came and went. I fitted a new dual flush toilet in mid feb and the mark is still there & today it’s particularly bad. I’ve checked under the floorboards and there are no pipes etc underneath which could be a potential issue. It’s dry on the lath & plaster but slightly damp on the floor joist.
All I can think is that condensation is forming on the inside of the stand and it is the dripping down the inside onto the floorboards. It’s bone dry under the cistern.
We do have a small towel radiator relatively close to the toilet but we haven’t had the heating on since Tuesday.
My plan this weekend is to take it all apart and see if I can pinpoint the issue but I’m fairly confident the toilet itself is water tight and it is condensation but not sure how to combat it. Any advice would be appreciated!! Ps excuse the state of the bathroom, we are still in the process of decorating etc

 

[oldbuffer]

1. If the room is heated, unlikely to be condensation.
2. I'd suspect:
2a. The seal of the doughnut washer between cistern and pan.
2b. If fitted, the seal of the bolts inside the cistern holding it to the pan.
2c. The seal on the inlet valve where the white plastic nut hold the valve to the pan.
2d. The cistern not being fitted square to the pan, or rocking on the pan and allowing intermittent leaks through the doughnut.
3. However, given that the mark "came and went" while there was no WC in place I would also be checking:
3a. Under the floor and along the joists for signs of water coming from other sub-floor sources.
3b. Checking the ceiling above the WC for signs of leaking / discolouration.
4. I's suggest removing the screws securing the WC to the floor, drying the floor as well as possible, then putting a large sheet of polythene under the WC before re-securing it. If water then forms on the plastic, you will know whether the source is above or below the floor.

 

[Mac1291]

That’s great, thanks @oldbuffer