I got a number of emails before Christmas about boiler testing, specifically the testing of small boilers. Several boilers have been advertised recently, either standalone or installed in locomotives, with a somewhat mealy-mouthed claim that the vendor is unsure whether they require a test due to their size (and this includes, it must be said, some sellers who on any other day of the week claim to be experts in the field...).
Now I can't personally see what you save by not testing a boiler, other than about five minutes and a pint of water. However, if you have a (very) small boiler and would like to exercise your right not to test it, the latest club rules exempt boilers with a capacity not exceeding 1.5 bar litres. So, for something like a Stuart 500 series boiler running at 60psi, which is pretty much 4 bar, total capacity would have to be 375 cubic centimetres or less (and for the Stuart, it isn't - so it needs a test).
To avoid testing, you need to get down to seriously small boilers - something like a Gauge 1 tank locomotive (the Roundhouse "Lady Anne" sitting on my desk at the moment has a capacity of about 300cc and runs at 40psi, or 2.7 bar - total capacity is under 1 bar litre).
Having said all of the above, at least pull the safety valve out once a year to make sure it isn't crudded up inside and the ball hasn't stuck fast to its seat (and about one in three of engines that come in here that haven't run for more than a year need attention to their safety valves).