short circuit test and resistance to earth test on combi

[cobra]

hi all
if i do a short circuit test on combi boiler between live and neutral when isolated, if i find a short circuit then i believe that i am supposed to disconnect wires from pcb to each component and test wires and component for short circuit, but how do i test for short circuit on wires and components that do not have a live and neutral ie different colour wires ie thermister or air pressure switch.
problem 2 when doing resistance to earth checks between live and earth at combi terminal and find a fault (assuming live to earth test means live leaking to earth ) how do i find/ isolate the wiring at fault ie could be wiring ie switched live or some other live wire but may not have no earth. hopefully this makes some sense to you. did a manufacturers course a while back and was shown the the 5 tests before working on combi, but wasnt shown how to further this ie to isolate and find faulty wiring or component and i was probably too flustered at the time to ask this question.
thanks again although relatively new to website been given lots of good guidance and knowledge

 

[armourer]

I maybe misunderstanding your question but I would just turn power off and with one lead of the multimeter on incoming earth (or even chassis) and the other lead against the live and neutral terminals of any components. any continuity would show as a short.

If you are looking for a short between live and neutral. one lead on live and test against the neutral terminals.(some components will give continuity but then look at resistance values across components.

 

[diamondgas]

Hi Cobra, Testing individual components to see if they're shorting is done as you mentioned, isolate the part and test. Doesn't matter whether the wires you're testing are live or neutral as your wanting to find out which component/wire is at fault! It helps to know what your expecting to get when testing so that you know if something is not right. A great deal of combi wiring is now low voltage/DC voltage. If you're getting into fault finding for the first time it can help ro familiarise yourself with the 'bits and bobs'. If you can, get hold of some faulty components and test them out against their new counter part to see the differences. Likewise familiarise yourself with thermisters and the like. I use to tale home all sorts of parts and mess about with them so that I could undertand how they operated! In fact just the other month I stripped down a Duotec fan to work out what was causing E160.

Best advice I can give is practice, practice, practice....! Make all the mistakes you can outside of the customers home but get your head around how things operate and their purpose in the sequence of events leading up to and maintaining a source of heat!