Boiler leaking from ... well, that's what I'd like to know!

[Neil Sutherland]

Users report symptoms, fitters replace faulty items, but engineers will diagnose & identify the cause before deciding what to do.
Do you know what caused your fault?

You are absolutely right, of course. Unfortunately many tradesmen are not as well trained or experienced as some of those on here. That's why so many of us ordinary punters end up here with our questions. Last time I asked a local firm for a diagnosis I ended up spending £250 on a new secondary heat exchanger which made no difference. On this forum I learned that what I needed was a couple of non-return valves for a shower mixer, which I was able to fix myself. Until standards in the wider market improve I shall remain grateful to the experts on this forum for their advice!

PS No, I don't know the ultimate cause of the problem!

 

[Wirdy]

A tale of woe. A good heating engineer will talk to the customer, will diagnose a problem correctly first time and fix it, OR inform the customer that it could be more than one part at fault & seek your approval to proceed with the fixing.
Maybe next time ask why a part is being changed and what happens if that part doesn't fix the problem? Does the old part get refitted? If not, is it trade price & free fitting on the unrequired part?, etc. It's a reasonable question that a decent engineer will not mind answering if asked in the right way.
Trouble is, most people are clueless or don't want to know & just want their plumbing/heating /hot water working again & are happy to pay whatever. Sounds like you want to know & have a good understanding of your system so you should be able to spot a poor engineer; maybe next time just pay them a reasonable amount for their call-out fee & show them the door if you're not happy with what they propose.
Good luck with your fix.