Best rust remover is...

[hotrodder]

Citric acid decomposes at ~ 175C i think. If the purifier is all stainless inside i doubt it'd damage anything if you left it running for a little while with a 10% solution in it. If there's plastics inside it i'd treat it like a kettle personally- switch it off before it starts to boil and leave it to soak for a while

FWIW at the bottom of pg2 Russell Hobbs say

We recommend cleaning your kettle with citric acid. Boil a litre of water, add 25g of citric acid and leave it to stand for 15 minutes.

and here's a generic cleaning/descaling stuff with citric acid recipe sheet... http://www.mikewye.co.uk/K-Citric%20Acid%20950.pdf

AIUI while orthophosphoric acid is a specific flavour of phosphoric acid (aka E338 for food grade stuff) it's what the vast majority of phosphoric acids are i.e. the type you get unless otherwise specified? Only way to be sure is to look at the small print/msds sheets for HP3O4

 

[spock500]

Thanks for that informative post hotrodder, I have saved the pdf for reference.

Cheers,

 

[w44nty]

Best rust remover is simply an angle grinder!

 

[Frontstep]

Yes as long as you cut off the rusty bit.

 

[Adem88]

What about small stone chips with rust

 

[Frontstep]

Good point, rust remover first then flap disc or soda blast.