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Ecodan Cascade System Problem: DHW Heating Stops UFH & Pool Output

fosterl2 · 2026-02-02T16:13:10Z

I have a new 2 x 14kw Ecodan system, that is required to supply DHW, UFH, rads and swimming pool heating. The two pumps are currently set up in a cascade configuration with 3 x FTC7 controllers (1 master and 2 slaves). The plumbing configuration for DHW is the version where the output from ASHP1 is diverted via a 3-way valve to the DHW tank when required. When the valve is not operated, the flow out then goes into the same buffer tank that ASHP2 feds, to then service UFH, rads and swimming pool heating, and on the output of the buffer tank is where the flow thermisters are located. The issue I have is when the system does DHW heat up, the logic decides after a short while that ASHP2 is not needed to get DHW up to temperature, so stops all output from ASHP2 (even though there is no plumbing for ASHP to DHW). This is clearly seen in the stats, as when DHW heat up starts, after a short duration, the flow temp out of the buffer tank is seen to rise to DHW level, and not 40ish degrees that UFH is set for. DHW heat up is set to allow up to 2hrs for heat up, and then drop back to UFH. The DHW does not always reach the tank (300lt) temperature setting of 55 degrees in the 2 hr period, so can go off for 30 minutes, then try again to reach target temp. Whenever DHW is heating, for the vast majority of the time, UFH is not being fed with hot water, and consequently the house / pool cools. Although by using the prohibited periods I can keep UFH on by not allowing DHW heat up, I end up running out of DHW by lunchtime. I am about to have the installer remove the cascade / master / slave arrangement so both ASHPs are controlled totally independently - i.e. ASHP2 will do UFH with no knowledge of DHW, and ASHP1 will do DHW, and then join in with UFH when not doing DHW, but with no knowledge of ASHP2. Before going ahead with this, I was wondering if anyone knows about the settings for getting the cascade set up to work where it will feed DHW from ASHP1, while at the same time allow ASHP2 to properly service UFH. Mitsubishi are adamant that the cascade set up is best for the requirement of all the DHW, UFH, rads and swimming pool heating, but are unable to say what settings will allow me to have UFH from one ASHP while the other is heating DHW. Thanks in anticipation... Lee

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Air Source Heat Pumps (ASHPs)

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fosterl2

(@fosterl2)

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Joined: 7 months ago

Posts: 16

Topic starter 04/02/2026 2:17 pm

@f1p Just checked again (with different glasses on!) and they are sliders, not rockers, and set correctly.

Looks like separating the cascade will be the way to go.

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fosterl2

(@fosterl2)

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Posts: 16

Topic starter 24/02/2026 10:16 pm

The issue seems to be solved: I found that the plumbers had routed the flow return from ASHP1 into the flow return of ASHP2, hence the whole system was behaving very badly.

I had to get the cascade removed to work it out, as there was only 1 set of thermistors - once the flow and returns of each ASHP could be monitored independently, it was pretty clear that there was a plumbing issue. Now the DHW ASHP is getting its proper flow return, the tank heating time has changed from not always being able to heat to target in 2hrs, to getting to 50 degrees in about 45 minutes!

I think the hardware supplier got the hump when asked to remove the cascade wiring (they took the master controller away...) so don't think I'll be asking for it to be put back in - with matching settings, the two ASHPs seem to be playing nicely, but the pool and pool room rads are not yet connected.

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F1p

(@f1p)

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24/02/2026 10:24 pm

@fosterl2 operationally that's a great outcome!

I wouldn't be too pleased them taking away the master FTC7 with a retail price around £940 though!

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fosterl2

(@fosterl2)

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Topic starter 24/02/2026 10:26 pm

@f1p Indeed - I am just waiting to see if I get sent a bill for removing the cascade, but intend to either ask for a refund, or a return of my property and have it as a cold standby!

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fosterl2

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Topic starter 24/02/2026 10:31 pm

The next challenge will be getting 60mCu of water warmed up! - I assume for the initial heating, take the weather compensation off, fix both flow temps to perhaps 40 degrees and run it during the day to maximise efficiency.

Any thoughts on how long that volume of water would take to around 25 degrees?

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F1p

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