This sounds like a question for the legionella control association

Part one of competence is knowing when you are not - so good on you for being initially critical of yourself. Technically speaking the law has not changed and the new ACoP is not making any new demands, just highlighting that they were always there. Competence for a legionella risk assessor is really rather complicated. I personally think that they are some of the most complex assessments that can be regularly come across (without moving into the more specialist fields associated with higher hazard premises/activities). COSHH is always more complicated than many people realise...except those who regularly read this forum! The LCA don't set any competence standards so wouldn't be able to easily assist, and unfortunately the rather glib answer is that member companies of the LCA need to determine their own competence standards which they then need to meet. But bear in mind the following from BS8580 ..assessor...'should be able to demonstrate that they have specialist knowledge of Legionella bacteria, relevant water treatment and the water system(s) to be assessed and that they are competent to carry out the necessary surveys, measurements and sampling.'. So this includes knowledge of microbiology, water chemistry and plumbing/engineering in addition to health and safety and associated practical skills. HOWEVER I'd like to keep this in check since you've clearly indicated that you're considering domestic premises. The ACoP and HSG274 Part 2 describes most water systems and I would presume that you're looking at fairly simple 2/3/4 bedroom properties with fairly straightforward hot/cold water systems in regular use. Following and applying the guidance will most likely see you through - particularly if you can see the management risks that go beyond day to day legionella control. 95% of legionella control is keep it clean, keep it hot/cold and keep it moving...the remaining 5% is the ability to spot those situations outside of 'normal' which require extra control measures. I consider it unlikely for these to arise in most domestic properties. Do you feel confident that you could identify situations such as these for which you could bring in extra help as needed? Cor I whizzed through and wrote that ... and then realised its super wordy. Apologies!

Is this an attempt for the HSE / LA to enter your property without warrant similar to we think you may be storing too much petrol. As far as I am aware there has never been an outbreak from a private dwelling.

I rent a house so can the HSE demand to come in to inspect my heating system and perhaps if it's not convenient I am fined for obstruction ?

It appears to me the HSE / LA s may be encroaching more and more into domestic premises. So can they demand entry to my rented house yes or no ?

Manners and logic I find are interrelated therefore I ask again can the HSE demand entry to a rented house against the domestic tenants wishes to inspect the water systems yes or no ?