We have our combi down at low temperature flow and it’s been successful for a while. Not had any problems with parts and it’s been running well for around 4 years now. 
I know some have extended warranty so perhaps the manufacturer prefers to be more cautious. 
Ours is a Worcester Bosch and I’m fairly sure it has a system to prevent any corrosive material within the flow. 

I have seen problems with corrosion in older condensing boilers usually where they have long flues and poor installation. Also my experience was with system boilers not combination boilers. If a boiler is installed correctly it should be able to handle the condensate from low running temperatures. 

How low? And is it a condensing boiler?

Many heating flows are set in the 70s or even 80s so as to warm the room quickly, and the radiators get too hot to touch. You particularly don’t want that if you have youngsters about.

Generally 50-60 is the most efficent flow temperature for a condensing boiler,
Techie link about flow temperatures and efficency.

Corrosion? Even a thin metal flue is unlikely to corrode through for years and should last the lifetime of the boiler.
When it comes to the rads, piping, and the boiler itself then a lower temperature is actually beneficial and results in lower rate of corrosion. There are other advantages too.
Techie link about corrosion and other advantages of a lower flow temperature.

Ihave mine on 55-60 flow normally and nudge it up to 60-65 when it’s colder winter. (My wall stat is normally set at about 19.5, my TRV settings vary depending on the room).

Totally agree with ​@Nukecad . Lower boiler flow temps (with a combi boiler) will give a more even heat and reduce overshoot. It may take a little longer to heat rooms but once there the room temperature should be more stable.

Regarding the condensate: they are DESIGNED as condensing boilers. The whole idea is that they recover heat when producing the condensate, which is what makes them more efficient.

Just checked our system: Boiler flow temperature 47°C, lounge radiator 38°C, outside temp 4.6°C and everything is working fine.

If you are thinking of moving to a heat pump in the future then this is a good exercise, as it will indicate which rooms may have problems (with undersized radiators) at lower flow temperatures. Slowly reduce the flow temperature and see if any rooms end up cold, then increase by a degree or two.

I have always run my boiler at between 50°C and 60°C and it is now 16 years old and still working well!

Thank you all for these answers. It’s a shame the gas engineer gave out misleading information.
I had a similar comment from a British Gas engineer who serviced a boiler for me (not mine as I have a heat pump). He also said it shouldn’t be run at a low temperature, he shook his head in disagreement when I insisted it was.
Maybe I attract these naysayers as it was only the other week in the same house that I was told by an electrician not to get a smart meter .

I think it’s just a case that these people are too busy doing the job to keep up with what has changed and improved in the underlying technology.

So while their knowledge about gas fitting regs, and wiring regs, should be up to date their knowledge about how best to use the technology effeciently day to day can be 10 or even 20 years out of date.

You see it in many areas of life, advances/changes happen so quickly these days that they soon outstrip the 'common knowledge'.

PS. Always check the date on anything that you read on the internet, it can get outdated very quickly but still looks brand new.