Notifications

Clear all

Joining the Renewable Heating Hub forums is completely free and only takes a minute. By registering you’ll be able to ask questions, join discussions, follow topics you’re interested in, bookmark useful threads and receive notifications when someone replies. Non-registered members also do not have access to our AI features. When choosing your username, please note that it cannot be changed later, so we recommend avoiding brand or product names. Before registering, please take a moment to read the Forum Rules & Terms of Use so we can keep the community helpful, respectful and informative for everyone. Thanks for joining!

Does legionella cycle also heats up radiators?

Air Source Heat Pumps (ASHPs)

Last Post by Mars 2 years ago

8 Posts

4 Users

3 Reactions

1,923 Views

RSS

bbmorales

(@bbmorales)

New Member Member

Joined: 2 years ago

Posts: 3

Topic starter 08/06/2024 8:17 am [#1573]

Hello. Beginner's question:

I have a system with a ASHP and a hot water tank.

When the legionella cycle (Friday 1pm for 1 hour) kicks in my radiators also heat up. Is this supposed to happen?

I am suspecting the valve that controls where the hot water from the pump goes (diverting to DHW or Heating) is not working well, and DHW is leaking to the radiators.

Quote

Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4474

08/06/2024 9:04 am

Welcome to the forums @bbmorales

No, that shouldn’t be happening. It sounds like you’re on the right track with your diagnosis though. During the legionella cycle, only your hot water tank should be heating up, not the radiators. This suggests that the diverter valve may be faulty and allowing hot water to flow into the heating circuit. A photo of the diverter valve would be helpful.

The other question this poses is that I assume your heating is off at the moment and you’re only using your heat pump for hot water production. So why is your system coming on at all and distributing heat to your rads. Does your circulation pump come on when the legionella cycles starts?

Get a copy of The Ultimate Guide to Heat Pumps

Subscribe and follow our YouTube channel!

ReplyQuote

bbmorales

(@bbmorales)

New Member Member

Joined: 2 years ago

Posts: 3

Topic starter 09/06/2024 8:47 am

Hi @editor Mars, many thanks.

Regarding the images, I've uploaded two, hopefully this gives you an idea of the system.

Regarding your other question

"Does your circulation pump come on when the legionella cycles starts? "

Apologies for the question, but where is this pump and how to I verify this?

I have not disabled completely the heating, but I can try doing so next Friday (disable completely the heating, leaving on only DHW).

Thanks for your help!

ReplyQuote

Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4474

09/06/2024 9:24 am

@bbmorales let's backtrack a little bit. Can you please share more information about the system you have (brand and model of heat pump would be a good starting point)? We'll need to ascertain whether your heating is in fact off.

Get a copy of The Ultimate Guide to Heat Pumps

Subscribe and follow our YouTube channel!

ReplyQuote

Morgan

(@morgan)

Noble Member Member

Joined: 5 years ago

Posts: 698

09/06/2024 4:30 pm

@bbmorales

There is no need, imo, to run a legionella cycle as often and it would be better run during the night on cheaper rate electricity. The ASHP heats to 50c and the immersion takes over to 60c. Expensive on day time rate on a weekly basis. Needn’t be for as long as an hour either so far as I know.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.

👍

ReplyQuote

HughF

(@hughf)

Honorable Member Member

Joined: 4 years ago

Posts: 489

15/06/2024 8:24 am

Faulty 3 port diverter….

Easiest fix is to disable the legionella program.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

👍

ReplyQuote

bbmorales

(@bbmorales)

New Member Member

Joined: 2 years ago

Posts: 3

Topic starter 15/06/2024 9:19 am

Hi All, thanks for your answers.

@editor

I have a Vaillant AroTherm plus 5kw.

Regarding the legionella cycle:

@hughf I had the impression it is important to do the cycle to keep bacteria from growing. Why would you disable it completely?

Thanks

ReplyQuote

Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4474

15/06/2024 1:57 pm

@bbmorales it's a personal preference and depends on the likelihood of bacteria proliferating in your tank. We run a Legionella cycle every two weeks. Since we work from home and use hot water frequently, the water in our cylinder is constantly being drained and replaced, preventing stagnation. This routine works for us. However, some homeowners choose to turn it off completely.

Get a copy of The Ultimate Guide to Heat Pumps

Subscribe and follow our YouTube channel!

ReplyQuote