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ASHP using its immersion, but I don't know why

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Air Source Heat Pumps (ASHPs)

Last Post by Mars 1 year ago

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Tufty

(@tufty)

Estimable Member Member

Joined: 3 years ago

Posts: 54

Topic starter 04/09/2024 6:02 pm

Hi all,

Each month I check my meter readings - on the heatpump and also my consumer unit.

Ive never needed to use the ASHP immersion heater, so that figure has been 0 for a couple of years. But since Jan 2024, the immersion has been using about 5kwh per month; and has been progressing to about 11kwh last month.

It shouldnt be using any immersion (especially becuase I only have DHW on in the summer months!). It didnt for the 2 previous years. Theres been perhaps one or two times where Ive has to quickly heat some water becuase Ive had guests to stay, but apart from that I just let the heat pump heat the cylinder once every 48 hours, which is fine for my use. (I live alone).

Is there a setting somewhere that may be using the immersion?

Heres some photos which Im hoping gives you an idea of its current settings.

Any guidance or insight would be gratefully received. Thankyou.

This topic was modified 1 year ago by Mars

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Anonymous 5011

(@Anonymous 5011)

Joined: 3 years ago

Posts: 562

04/09/2024 6:16 pm

Has legionella function been switch on?

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Tufty

(@tufty)

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Joined: 3 years ago

Posts: 54

Topic starter 05/09/2024 5:11 am

@johnmo Ah! Thats a very good question! I will go and check! (that will be egg on my face if I accidentally turned it on)

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Morgan

(@morgan)

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Joined: 5 years ago

Posts: 660

05/09/2024 7:32 am

@johnmo are you suggesting the legionella function should not be switched on? I've always assumed that it must be switched on.

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.

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Anonymous 5011

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Posts: 562

05/09/2024 8:05 am

Posted by: @morgan

↑

@johnmo are you suggesting the legionella function should not be switched on? I've always assumed that it must be switched on.

Legionella prevention is a risk based activity. It all depends on the temperature you store your water and how quickly water is refreshed. Heat Geek have a quite good write up on the subject, well worth a read.

For example we store at 50 Deg all the time, so any bugs naturally die off at that temperature (after a few hours), we also consume the water in the cylinder, so it's not sitting for long periods without being refreshed.

You go through the risks, your personal circumstances and make your own call.

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Mars

(@editor)

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05/09/2024 8:08 am

More on the subject of legionella here: https://renewableheatinghub.co.uk/legionnaires-disease-home-hot-water-understanding-risks-and-prevention

Get a copy of The Ultimate Guide to Heat Pumps

Subscribe and follow our Homeowners’ Q&A heat pump podcast

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Mars

(@editor)

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Posts: 3643

05/09/2024 8:09 am

@tufty did your ever get to the bottom of the issue? Was it a legionella setting or something else?

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Subscribe and follow our Homeowners’ Q&A heat pump podcast

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Abernyte

(@abernyte)

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Posts: 243

05/09/2024 8:12 am

There is no requirement for the legionella cycle in a domestic setting. Different if it was a commercial installation where L8 regs apply. The chance of catching legionella from a modern unvented system is vanishing low. Chlorinated water, no unflushed dead legs, sealed DHW cylinder and plate heat exchanger make it a theoretical risk rather than a practical one. If you are very frail or vulnerable then an abundance of caution suggests you turn it on, otherwise don't bother.

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Tufty

(@tufty)

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Joined: 3 years ago

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Topic starter 05/09/2024 8:53 am

@editor Yes. I checked this morning and the legionella setting is disabled. (I turned it off soon after the ASHP was installed because at the time I felt I was very low risk). So Im not sure what else could cause the immersion to come on(?)

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Anonymous 5011

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Joined: 3 years ago

Posts: 562

05/09/2024 10:25 am

I notice your DHW looks to be at 55. It could be you are trying to heat the DHW too high for the heat pump on it's own, so the immersion kicks in to finish the heating.

Thing that change over time, the condenser gets blocked with debris etc. worth checking and hose it clean. Main system filter strainer getting blocked slowing max flow rate.

All worth looking at.

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Gary

(@gary)

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05/09/2024 10:50 am

I agree with Johnmo, 55C is right on the limit of immersion being required for the Ecodan, did you increase the DHW set temp in Jan 24, as that would explain it. If you drop it back a couple of degrees and see if it stops using the immersion than that's the cause.

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Morgan

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