https://www.youtube.com/watch?v=tlYdUPOPZDM

Read also what I wrote in another topic about the Cryptosporidium outbreak which affected mains water supplies in the Brixham area of South Devon.

There will be circumstances in which legionella bacteria are present in the water supply. The point of the anti-legionella schedule in heat pumps is to prevent the DHW tank sitting at the temperature range where they can rapidly multiply.

It's the speed of bacterial culture growth which presents the problem.

Do you know the classic biology question which reads:

"A jar of culture medium is injected with a bacterial sample which exhibits cell division every minute.
After an hour, the jar is 'full' in that it is 100% saturated with bacteria.
When did it reach 50% saturation?"

That leaves us with the question of whether a professional installer or a heat-pump manufacturer could be held liable for equipment which didn't offer an anti-legionella provision.

I can only share what the installers have told me: they enable legionella cycles on installed systems to avoid any long-term liability. However, as a homeowner, if you choose to turn off the legionella cycles (as we have) I don’t believe there’s any liability on the homeowner. Interestingly, every installer I’ve spoken to who owns a heat pump has their legionella cycles turned off. That’s not to say it’s the right or wrong approach, but it’s worth noting as a common practice among professionals and the associated risk.

The Exeter-based office of Public Health England didn't appear to see prevention as part of their remit, although they would expect to be involved if someone suffered from the infection. They stated that this could be an issue to be handled by the Environmental Health Officers at the district/borough level of local government.

To some extent that makes sense because it is District Councils who administer planning permission and building control issues. However, in the case of heat-pumps, we already know that the vast majority of installations do not comply with Part-L of Building Regulations, and Councils take no action.

When there have been accounts of legionella infections in the press, they invariably concern members of the public picking up the bacteria in water droplets from heating/ventilation units owned by companies or organisations. The Health & Safety Executive therefore pursue a prosecution. The same laws apply to all property, which leaves open the possibility of a householder being prosecuted if their heat-pump installation gives rise to Legionnaires Disease. Many home insurance policies already have clauses which cover legal costs, but I wouldn't like to risk such a prosecution, and any fines are unlikely to be covered.

That leaves us with the question of whether a professional installer or a heat-pump manufacturer could be held liable for equipment which didn't offer an anti-legionella provision.
That's less likely.

If a roof tile falls off and hits someone at your front door, then the householder is liable and would usually make a claim under the house insurance policy.

That responsibility is true even if the tiles had been recently fixed by a roofer.

This was a topic we talked about in one of our podcasts, where a panelist mentioned that homeowners aren’t legally required to run legionella cycles. However, there is a legal requirement for businesses to do so. That said, it’s always best to verify this information to ensure accuracy.

Regarding legionella control, there isn’t a specific “kit” for this. Most of the time, the heat pump’s control panel will include legionella settings. When the parameters are met, legionella cycles are usually handled by the immersion heater in the hot water cylinder. Some heat pumps also have an immersion heater within the unit itself, which can be used for defrosting and running legionella cycles.

Could you remind me which heat pump brand you’re using? 

My County Councillor has taken up this matter with the regional office for Public Health England, and I've received a response.

What we can do here is to provide them with background knowledge of what happens when power to heat-pump is cut.

If a Power-outage extends over a time period when an anti-legionella cycle would've occurred, are HP controllers 'aware' of that?
When power is restored, does it provide any indication that the cycle has been omitted?
Does any HP run an anti-legionella cycle as a precaution when power is applied?

Does any HP take action if it's sensors detect that the temperature in the DHW cylinder has fallen within the danger zone for legionella?

DESNZ's Public Consultation is asking if there should be a Directive to Manufacturers to make HP models such that they have particular features to better suit them for DSR operation.

The Consultation asks specifically about whether HPs should be able to modulate their output in response to Explicit-DSR commands?

And they want us to comment on whether DESNZ should set a max limit on how long a heat-pump should be switched off due to Explicity-DSR commands.