Sorry Graham - a misunderstanding I think - my screen showed a "random order" as it updated the thread, which now appears logical. Blame the www
Caveat emptor Rob - a little common-sense helps too.
The whole testing thing is a can of worms, or so I read. Actual valve testers do not generally measure any valve in an operating condition, and many people just measure heater resistance and say all is OK based on that.