Willis powered UFH Electrical Fault - HELP

[Triassic]

I've finally got my Willis powered under floor heating working.
 

But!!  The earth leakage device on the split fuse board trips randomly.  I switch the pump and Willis heater on and it will happily work for 10 to 20 minutes then trips for no obvious reason. I’ve double checked all the wiring and swapped the earth leakage device. Has anyone experienced similar, what should I be checking/replacing next?

[ProDave]

You need to do an insulation resistance check with a megger, most likely the immersion heater element is faulty.  such faults often only show when the heater gets hot.

[Triassic]

Are the elements easy to change?

[dpmiller]

generally the modern willis is a soldered-up unit, it's rare to see one that has a seperate shell and element.

[Triassic]

17 hours ago, dpmiller said:

generally the modern willis is a soldered-up unit, it's rare to see one that has a seperate shell and element.

Yes they are! So no repair possible. Having checked the insulation resistance of the pump and the Willis I’ve concluded that the pump I may be at fault. Just off to get a new one.

[Triassic]

Having done some tests I had an hunch it was the pump at fault, it was second hand! A new pump fitted and everything is now running a dream.

Edited January 1, 2021 by Triassic