RCD Tripping having added an additional circuit

[Jagman]

I have a 12way consumer unit which is fitted with:
7 x 32 amp MCB which cover: 4 ring circuits, 1 circuit for the garden which includes a hot tub, 1 oven circuit and 1 going to the hob.
3 x 6 amp MCB covering the lighting circuits.
2 x 16 amp MCB one for the E/Heater and the other for the underfloor heating in the kitchen.
The total installation is covered with a 63amp 30ma RCD. all was fine until we added the underfloor heating. we now have the RCD tripping at different times during the evening or early morning. I have double checked the underfloor heating circuit and it is fine. Am I overloading the RCD? should I up rate to a 100amp? I have found that if I switch off any of the major circuits the tripping stops

 

[pdcelec]

I have double checked the underfloor heating circuit and it is fine.

What are the insulation resistance readings for this circuit?
What Loop impedance did you measure?

 

[Jagman]

The output is 1300 watts and the resitance is 44ohms

 

[Qedelec]

You misunderstood pdcelec.
He asked what is the insulation resistance.
Measured with an insulation tester applying 500V @ 1mA between all conductors.