get yourself one of wolesley part centres' digital multi meters.
very reliable, has big display, backlight, live voltage warnimg on red led over screen, decent leads, tough as old boots, and very reasonably priced. i prefer mine to my old fluke meter.
as for fault finding, ive been an oil fired boiler engineer for a VEEEEERY long time, and still find new faults every week.
thats why i love being a diagnostic breakdown engineer!
if you chaps want any help on system faults, especially oil fired related, drop me a line and i'll be glad to help out.
fault finding really is the best part of our job, never gets boring!!
heres an easy one to start you off....
customer calls and complains of no central heating but has hot water, system is 'y'plan fully pumped.
where do you look first??
mark