Peculiar RCD?

[Cirrus]

Did a C/U change yesterday and used a Crabtree dual RCD c/u. Did a pre-test (as I always do) and every circuit was fine with the exception of some low results on the sockets circuit on Ir. (around 10m ohms ). Put new board in place, continued with testing and everything was fine. Now, the second RCD has started tripping out (not aggressively) after about 15 mins of being on. Nothing is drawing load to take the RCD out - it just seems to randomly drop out. This RCD only controls shower pump, w/c lights and also immersion. Just seems strange that it holds and then for no reason I can see, it trips out.

Any ideas?

 

[Evans Electric]

Check the immersion ,Cirrus.

 

[Cirrus]

Thanks, disconnected it and waiting to see.

 

[Cirrus]

Still holding in after 80 mins so may be the problem.

 

[Badger]

could be the heating element going to earth after it starts heating up