One tip to remember when you're asked to do a visual inspection in ACS assessments is to really look; not just glance at things. Whether it's gas pipes or flues, look closely and in detail, not just at the front but around and behind. Take your time.
With the pipework task I would suggest checking the following:
Sleeving: if the pipe comes through the wall is it sleeved correctly? Is the sleeve sealed with the correct type of compound?
Electrics: is the pipe too close to cables? Is it to close to electrical equipment such as consumer units and electric meters?
Clipping: is the pipe supported at the correct intervals? Are the clips of the correct design?
Open ends: is there an open ended pipe or fitting? This would include pipe / fitting that has been capped with an incorrect fitting.
Compression fittings: have they been used correctly within the restrictions of their use?
Is there any damage or corrosion visible on the pipe?
Earth bonding: is it in the correct place? Has the correct cross-sectional area wire been used?
Is any pipe obviously undersized (i.e. such that you can tell visually, without calculation)?
Fittings: are they suitable for gas?
Meter anaconda: is it the correct side of the meter?
ECV: does it fall to off? Is it unobstructed? Are the ON / OFF positions labelled?
Are any flexible connectors used correctly?
These days, as well as spotting the faults you also have to classify them within the Gas Industry Unsafe Situations Procedure. Make sure you learn the correct classifications, and whether any of the faults would be RIDDOR reportable (generally ID faults which are caused by bad workmanship).
