Ok - so spend Â£450 on a powerflush to save the pump that would cost about Â£80 to replace. I'd understand a customer being sucked in - if they said it would damage the boiler that would cost around Â£1000 to replace.
Alot of plumbers like to do power flushes because it's quick easy money. If there's sludge/debri's etc in the system, then removing and flushing radiators - flushing pipework a few times hot and cold will remove most of it, or add system cleanser for the recommended time.
The key to prevent this is to add inhibitors after the flushing, this will prevent the build up again.
What's the problem with the system ? radiators not heating ? cold spots on radiators ? if everything works fine - a few flushes and inhibitors is alot cheaper and more effective.
The plumber was originally called out because the pump had gone. After replacing it , he found that the new one wasn't working as efficiently as a new pump should, so after investigation, he discovered all the sludge in the system - he showed me the stuff and it was pitch black with lots of debris in.
He says that unless the system is flushed through, the new pump will go again and the boiler will eventually pack in as it is having to work too hard to get heat around the system.
A power flush sounds logical to me, but then I'm a complete novice, so any further feedback much appreciated!
It's up to you, I would still try removing and flushing radiators and pipework flush a few times when the system is hot, get it so that the water is running as clear as possible.
Add sludge remover (sentinel x400) Â£15ish and use heating as normal it just says for a minimum of 2 hours, no maximum time. Drain and flush radiators and pipework a few times and add inhibitors (sentinel x100) Â£15ish.
If you are a capable DIYer the labour is free, so Â£30 worth a try.
You haven't said the heating is not working, that any radiators do not heat up or there are cold spots on the radiators. So you may have caught it where it can be saved without spending too much money on it.
Like I say it's up to you, but for Â£30 and say a maximum 2 days work, one day to flush and add sludge remover and one day to flush and add inhibitor - before spending Â£450 - i'd give it a go. You can't make it worse.