i think you are being harsh on zimmer, if he said to the guy 'it'll be 250 quid to sort', BEFORE he did the work, then its the customer who has the choice.
Most customers have got no idea what the repair entails and in desperation will often just accept a quote in order to have their heating/hot water working again...they're only to gratefull someone's turned up. They have a misplaced trust in the installer to carry out the repair for a fair and honest price.
It appears that this repair took no more than an hour or two, given a quality pump is around £50.00 then £200.00 labour is nothing short of a rip off. This over-charging really p****s off the good installers out there since it continues the stereotypical image of the industry...full of cowboys out to scam.
As you say manortim, you are new to breakdowns.....you will learn to despise these charletans and have no tolerance for them as you come across customers that have been ripped off time and time again.
It is up to the installer to explain the costs, likely parts needed and possible problems that will be encountered. Its often impossible to give an accurate qoute but I've no doubt zimmers did not tell the customer he would be charged £200 for just a couple of hours work.