Notifications

Clear all

Ecodan unable to hit legionella target temp - what's the consensus?

9jwr9 · 2025-12-17T08:43:41Z

Hi all, We have an Ecodan 14kw (PUHZ-HW14VHA2-BS) paired with Joule Cyclone Platinum 300l cylinder and a buffer tank. Heating is all working great, however the hot water cycle defaults to the legionella cycle every day, because the temperature maxes out at 59 degrees, and cannot reach the required 60. Temperature gets up to 50 degrees within 30 mins via the HP, then HP disengages and immersion kicks in and slowly (around 1hr) gets it up to 59 degrees. It seems as though the immersion then cycles, keeping the temp at a constant 59. Others have reported similar issues and it seems it was often an issue with the immersion thermostat having a max of 60 degrees, with a higher-rated replacement thermostat solving the issue. Others have talked about software within the FTC2 controller somehow instructing the immersion to cut out at 59, but that's a little technically beyond me. The thermostat for the immersion is a Thermowatt T105 RTS 3 (pictured) which, from what I can tell, should be able to well-exceed 60 degrees on the max setting (which I've moved it to). Does anybody have any further thoughts on this, or perhaps had the same issue and found a solution? Thanks in advance.

Page 2 / 2 Prev

Air Source Heat Pumps (ASHPs)

Last Post by ASHP-BOBBA 1 week ago

17 Posts

6 Users

3 Reactions

319 Views

RSS

9jwr9

(@9jwr9)

Active Member Member

Joined: 3 months ago

Posts: 9

Topic starter 17/12/2025 11:37 am

@majordennisbloodnok ah! Yes, I did see this video. As per my reply to @rhh2348, we don't have that controller unfortunately. We have an older one, which has no legionella settings available.. If we had the one in the video, I think we'd be sorted!

ReplyQuote

rhh2348

(@rhh2348)

Reputable Member Member

Joined: 2 years ago

Posts: 102

17/12/2025 11:46 am

MITSUBISHITECH.CO.UK "http://www.mitsubishitech.co.uk/Data/Ecodan/Controls/PAC-IF031B-E_FTC2/FTC2_IM.pdf"

mentions dipswitches to control legionella - one of the options is every 15 times DHW?

🤩

ReplyQuote

benson

(@benson)

Honorable Member Member

Joined: 2 years ago

Posts: 249

17/12/2025 3:00 pm

@rhh2348 ...maybe this option is what you want?

Alternatively the immersion heater may be controlled separately. If direct control is not required then DIP switch SW1- 4 should be turned OFF and the immersion can then be controlled via its own weekly timer as with FTC1.

ReplyQuote

9jwr9

(@9jwr9)

Active Member Member

Joined: 3 months ago

Posts: 9

Topic starter 27/12/2025 11:27 am

UPDATE: Thanks everyone who commened with suggestions here - all really appreciated. For those interested, the issue was with the immersion thermostat itself, as some people suggested. The thermostat had been calibrated (for reasons unknown) to max out at 60 degrees, which meant it was physically impossible for the water temp to go beyond that. I broke the little plastic restricter off it, turned it an extra quarter turn, and the tank then succesfully heated to 65 degrees, satisfied the legionella cycle requirement and we're all good now! 🙂

👍

ReplyQuote

ASHP-BOBBA

(@ashp-bobba)

Prominent Member Member

Joined: 1 year ago

Posts: 317

28/12/2025 6:41 pm

@9jwr9 Hi, yes this is the issue with every (stand alone Ecodan) when mixed with an alternative cylinder, we set them all to 60 Deg C and just make them keep that heat level longer to cover the burn. If you use a Mitsubishi cylinder they do not have a control stat on the element only an overheat and all of the control is done through the contactor. What happens with the stand alone Ecodan and an alternative cylinder is the contactor is still used but has another stat inline as part of the element.

AAC Group Ltd covering the Kent Area for design, supply and installation of ASHP systems, service and maintenance, diagnostics and repairs.
Professional installer. Book a one-to-one consultation for pre- and post-installation advice, troubleshooting and system optimisation.

ReplyQuote

Page 2 / 2 Prev