Rcd advice needed faulty or fault

[Stuportsmouth]

So had to fit a new shower as old one kept tripping the rcd after few seconds assumed the shower was to fault as made a buzzing noise and tripped, on fitting the new shower it had same faukt so checked pressure of water no issue then checked wiring at box also no issue so moved onto next possibiliy of short on cable.
Yes maybe should of used multimeter and tested each one out but easier as short run in walls so run new cable exactly the same.
So decided to wire a small flex with bulb holder on that trips rcd changed the 40amp mcb to a 16 amp tried light also trips could this be a faulty rcd its rated 80amp 30ma, we also tested the the curcuit with every mcb turned off with only shower circuit on and also tripped.

Any help would be greatly appreciated as would like to think in a 6 bedroom house with each room occupied that of rcd was faulty then it would trip as currently has approx 8 circuits on and only randomly started to happen nothing new has been added.

 

[Darkwood]

You know what don't care I can't here to ask a question just because I'm not qualified doesn't make me incompetent of knowing what I'm doing working with someone who's qualified from a young age and being overseen and checked on standards of work and also working on 3 phase and also being more than competent of doing so is more than some newly qualified electricians have in experience.
As most newly qualified electricians just goto college learn sit a test and have a certificate being trained alongside a family member rewiring houses at weekends and then working doing air conditioning from the age of 14 until I was 19 and being trained to a standard by a qualified person is more than anything on a piece of paper and all on this forum are so stuck up there as**s that I'll seek advice on a different forum

You asked a question of which the forum is here for but within few posts it was clear to members you are dabbling in things you are not competent to do, regardless of your onsite experience unless you understand the theory behind what you do then you are not competent to do it on your own, it is very evident from your responses you are far from competent, your using the wrong test equipment, you not following any recognised sequence of testing and you making guesses, replacing items and finding your still in the same boat, the most dangerous thing in our industry is a DIYer who thinks he is more competent than they actually are, 3yrs of college will be a massive eye opener for you then I would challenge you to come back and look back on this thread, trust me you would shake your head, considering you have a dad fully qualified I actually find it strange you have come to the forum after several failed attempts to rectify the issue, surely he would naturally be the first port of call especially with him having the correct test equipment.
You mention low water pressure caused the shower to overheat and tripped the circuit, you clearly are guessing again as showers have integral thermal overheat protection and this would operate if it overheated (not your mcb or rcd), this would either self reset or require replacement.

Like others have mentioned within the thread I also strongly advise you get a competent Electrician in to do the fault finding or aid you in finding it, as you have clearly shunned this advise on numerous occasions I only can come to the conclusion your ignorance to your own lack of competence is a danger to yourself, as the forum is here to give good safe advise.
I prefer the forum upsets and loses a member by giving safe advise than aid a DIYer who is clearly taking on more than we consider they are competent to do, your postings and remedies to your own situation are a massive beacon of your position and therefore on that note I am closing the thread!