So do I mate but only if I really can't fix something
surely that is exactly what "no fix, no fee" is.
I don't go out on spec.I charge for fault finding but only charge if I fix so the customer knows what the charge will be up front when the boiler is working.
I spent five hours on an old thorn Apollo BF years ago changed everything you can think off (no pilot was the fault) and still couldn't get it to work,even with the help of thorn's tech support who basically gave up,so I removed all of the parts I had fitted put everything back and walked away with not a penny.
Also,in the past,crawled about under houses to locate pumps and motorised valves (for free estimates)only to be told that the customer would get back to me once I had given him/her the price to replace/repair.