RCD Tripping When Either SFCU or timer goes off

[cyberjunction]

HI Guys

New to the trade and currently learning but in real need of help. I changed the C/U and the RCD keeps tripping although all tests came back fine. It is the Central heating that is doing it for sure as I have had the immersion on and turned off the central heating for the past 6 weeks with no problem. I changed the SFCU and timer ( same model ) just in case as they were both old. It happens intermittantly but usually when either the SFCU is switched off or when the timer switches off. If I flick the SFCU on and off it will trip about 50% of the time likewise with the timer clock. THis only happens once the boiler ignites and pump kicks in. ie if control panel is on but not calling for anything the the SFCU can be switched on and off without tripping RCD, only trips when control panel is power boiler/pump

I have checked for moisture, holes in cables, loose cables etc but pretty much stuck

Any help would be much appreciated, I don't have any experience at all with boilers, central heating etc. thanks

I should add there were no RCD's on previous C/U - thanks

 

[Octopus]

Have you ramp tested the RCD?

 

[cyberjunction]

hi
tried that all was fine, thanks anyway

have taken the thermostat of wall....and it does not trip......have link the therm wires so the c/H kicks in and again no trip....trying new thermostat later...just in case

cheers