The initial tripping was intermittent and would happen overnight. The system would operate happily for 3-4 days then trip out.One post seems to contradict the other here, you can't start the system but then it trips overnight
If a brand new RCD is tripping at that level I would be speaking to the manufacturer about a replacement, out of the box problems with RCD's seem to be getting more common in the last few years
This led me to believe that a fault had developed on one or more of the heating components as the customer was turning off the 2 top floor heating system and no tripping would occur.
It was only when I was on site and tripping happened that I made the discovery that the tripping would happen when the UFH called for the boiler to fire and the pumps started up.
On Friday the system would always trip with all the UFH systems on so the 2 top floor UFH systems were switched off.
After my initial discussions on here I asked the customer 2 switch off the ovens and the hob, at the wall, on that side of the CU. They then turned on the 2 top floor UFH systems and no tripping occurred.
It was left like this from 11:00 until 16:00, then they switched the ovens and hob back on with no tripping.
Until they got up this morning and the RCD had tripped.
I'm now heading down the path of cumulative leakage current. More testing required.