New British Standards relating to system water in central heating systems

The new BS 7593:2019  was  introduced in May 2019 to provide clear guidance on the preparation, commissioning and maintenance of domestic central heating and cooling water systems.


    • Q: Is it MANDATORY for installers to fit an in-line filter, or is it best practice?

A: BS 7593:2019 is a best practice document recommended by the plumbing and heating industry. The expectation is that in the interests of boiler manufacturers, professional installers, service engineers and Gas Safe Registered to follow the standard and maintain the high levels of service in the industry for their customers. This includes fitting an in-line system filter to be complementary to chemical water treatment to protecting and extending the lifespan of the heating system.

  • Q: What SPECIFIC installations does it apply to?

A: The document refers to all domestic central heating systems (new and existing), open vented and cooling systems.

  • Q: Do systems HAVE to be chemically treated? In what instances? Or again, is it best practice?

A: Part L Building Regulations stipulates that  wet central heating systems should be cleaned, flushed and inhibited when installing a new boiler and it refers directly to BS 7593 for guidance. The revised BS 7593:2019 document recommends central heating systems should be protected by dosing with high-quality chemical water treatment and fitting an inline system filter. Systems should be topped up with an inhibitor every five years or the quality of system water tested using a postal laboratory service or on-site test to ensure full protection against corrosion and scale. For hard water areas above 200ppm a scale reducer should be fitted.

  • Q: Do installers HAVE to test the water? What for, how often, what if it’s not good enough?

A: The document states it is mandatory to check inhibitor levels annually and re-dose a system after five years or perform a laboratory analysis or on-site test. If the inhibitor level test indicates inadequate levels of inhibitor, the system should be re-treated with a high-quality chemical water treatment.

  • Q: Is this British Standard MANDATORY for installers?

A: BS 7593:2019 is not mandatory but it is a best practice document recommended by the plumbing and heating industry. It is in the interests of boiler manufacturers, installers and service engineers to follow the standard and maintain the high levels of service in the industry for their customers.

  • Q: What happens to people who don’t apply?

A: Condensing boiler technology, which promotes energy efficiency and fuel saving has resulted in the miniaturisation of boilers. This means that the waterways in  modern boilers are smaller and more vulnerable to damage from circulating sludge and debris; causing premature system failure and breakdown. The major boiler manufacturers will use this standard as part of their installation and servicing guides to support extended warranty programmes, which benefit the consumer. Failure to comply with the new standard may deem the boiler warranty invalid.


Has your system water been checked? this can be done as part of a routine annual service of your boiler. Get in touch for more details......