It's vital to comply with your boiler manufacturers warranty.

247homecaresucure make statement of fact regarding manufacturers warranties...

Its spokes person said, "Your boiler’s warranty is always accompanied by terms and restrictions that must be followed for your warranty to be honoured. For example, suppose your central heating system is full of sludge (deposits caused by rust), and this sludge gets into the components of your boiler. In that case, the manufacturer may refuse to repair it."

Ref: https://247homerescue.co.uk/blog/boiler-warranty/

The below statements have been extracted directly from the manufacturer's warranty terms and conditions and can be read in full at the links provided.

Worcester Bosch Warranty & Guarantee.

4.2.7 Damage to the Product as a result of water quality or other external factors causing scale, sludge, blockages or associated costs of rectification.

https://www.worcester-bosch.co.uk/guarantee-terms-and-conditions

Baxi Warranty & Guarantee.

9. Any damage caused by hard water scale deposits or sludge resulting from corrosion.

https://www.baxi.co.uk › faqs › gen...
General boiler warranty information

Vaillant Warranty & Guarantee.

15. If any failure is caused by contaminated water in the boiler (e.g. blockages, or influences of flux residues, iron oxides, limescale, sludge etc.) the engineer’s visit becomes chargeable at the prevailing rates.

https://www.vaillant.co.uk/technical-pages/terms-and-conditions/

Ideal Boiler Warranty & Guarantee.

d. To de-scaling or other work required as a result of
hard water scale deposits or from damage caused by
aggressive water or sludge resulting from corrosion.
Indications that such work may be required include a
noisy boiler, cold spots on radiators, sludge in pipes
and poor circulation of the central heating system.

https://idealheating.com › I...PDF

Viessmann Warranty & Guarantee.

To be clarified.

Glow Worm Warranty & Guarantee.

15. If any failure is caused by contaminated water in the boiler e.g. blockages, or influences of flux residues, iron oxides, limescale, sludge etc. the engineer’s visit becomes chargeable at the prevailing rates.

https://www.glow-worm.co.uk/homeowner/repairs-and-servicing/guarantee/guarantee-terms-and-conditions-223455.html