Ecodan SIKA Flow sensor failure

[joth]

Since July I've been getting periodic L-9 "Low flow rate" system error on my FTC6 (for MITSUBISHI Ecodan PUHZ-W85VAA)

 

I've checked all filters etc and everything is clean and appears to be free running. The circulation pump is set to maximum flow rate (factory default, as it always was). I'm currently using it in cooling mode only (disabled DHW, doing that with immersion) and still happening. (When I had DHW enabled it happened more often in the DHW phase, but even happens without at a couple random times per day)

Using the controller "commissioning wizard" I see the flow rate was flickering on and off at 5l/min, which is about the lowest value it can sense.

 

Looking back through grafana, I see prior to May it would peak at about 12l/min but then steadily declined month on month until the errors started.

 

 

 

I've flipped dip switch 2-8 to say "no flow sensor" and the unit has been working fine for the last week. (Very needed as it's been very hot and the cooling is very desired by our guests!). Only downside is the output energy monitoring now gives bogus values (as it estimates it based on flow rate and temperature drops).

 

 

So questions

1. Does this sound like the flow sensor itself has failed? Any suggestions how to verify it is at fault? (Is this a reasonable thing to fail after 3 years use?)

2. Aside loss of energy monitoring, do you see big risks of further damage by using it without a flow sensor?

3. Any tips where to buy a new one? It's a SIKA VVXC9SNBUC00242P. (Mitsubishi won't talk to me as I'm not MCS + mitsu trained installer)

 

 

Edited August 16 by joth

[ProDave]

I had similar flow rate issues with my ASHP (different make and model) when first installed, and the only way I solved it was to buy and install an in line flow meter so I could see what flow rate was being achieved regardless of what the sensor said.  In my case it was only an on off sensor (enough flow or not enough flow) and I needed a real reading to see what was going. on.

 

I solved it by adding a second external pump to increase the flow rate above what the inbuilt pump could achieve.

 

The fact you have an actual measure and it has been decreasing, suggests there is an actual problem.  Which again is where an independant flow meter would help.

[JohnMo]

44 minutes ago, joth said:

I've flipped dip switch 2-8 to say "no flow sensor"

The heat pump will almost definitely have a flow switch which is activated on a low flow condition in order to self protect. Mine (not mitsubishi) doesn't measure actual flow, I can hook up an external flow meter, if I felt the need, but if it senses min flow via the switch, it shuts down.

 

I have an external heat meter to see what the actual flow is.

 

Are you on glycol? Either way have you checked condition of what is being circulated? If glycol based is it turning into a soup m

 

Looks like steady decline in flow rate, for both the high and low peaks - do you have zones switched off, or heating fluid getting more viscous?

[joth]

1 hour ago, JohnMo said:

The heat pump will almost definitely have a flow switch which is activated on a low flow condition in order to self protect. Mine (not mitsubishi) doesn't measure actual flow, I can hook up an external flow meter, if I felt the need, but if it senses min flow via the switch, it shuts down.

 

I have an external heat meter to see what the actual flow is.

 

Are you on glycol? Either way have you checked condition of what is being circulated? If glycol based is it turning into a soup m

 

Looks like steady decline in flow rate, for both the high and low peaks - do you have zones switched off, or heating fluid getting more viscous?

 

Was on glycol but added anti-freeze valves a year ago and I believe all glycol will be out of the system by now. I've had to drain and refill it several times due to other things going on. (Adding FCUs, adding volumizer, adding more bleed valves, probably something else).

When I washed through the system filter (fernox tf1) the discharge was perfectly clear looked just like tap water.

 

When I last filled it up last (Nov 2023) I put some misc inhibitor in (Sentinel X100) as there's no glycol to act as inhibitor. That's rated down to -2.5°C. the water never drops below 10°C so can't see that would be causing an issue. But, the gradual decrease in flow since May does corelate to the start of cooling season. If I can limp through to autumn it'd be interesting to see if heating-only mode undoes the problem.

 

Otherwise I'm wondering if there's a strainer somewhere else in the system that has got clogged. Maybe on the external flexi pipes.

 

Also to clarify the flow sensor (and the L9 error) are just on the primary circuit, which consists of: ASHP, pump, filter, 3-port valve*, LLH/UVC

So issues in the zones (UFH and FCU) shouldn't impact this flow.

 

* - the 3 port valve is a mid-position valve - yuck. I bought a diverter valve ages ago to replace it with, but when I went to fit it last week I found out I'd ordered 22mm but need 28mm. (The UVC is in 22mm which I measured, not spotting the reducer right where it enters the valve).

I've just received the correct size 28mm diverter and plan to install, but this was mostly to reduce my suspicion that DHW/cooling switch over was losing efficiency due to a sloppy mid-position valve change over.  I don't think it physically could be the cause of a reduction in flow rate.. But who knows.

 

 

 

 

 

[joth]

Hmmm well 10 weeks running it with the flow sensor disabled it seems to be performing just fine, so I'm still inclined to think it's a sensor failure. Ideally I'd borrow a replacement to test - they're not cheap, and a bit of a pain to get hold of.  I only really need it to get more accurate energy delivery estimates from the controller.

[joth]

Bit of an inconclusive update.

Got a replacement flow sensor today, but was unable to install as the pipework is clamped so tight around the existing one I can't open the threaded connectors out enough to remove it. Decided that's a job for after the holiday. But then noticed the instructions say it shouldn't be mounted up downward flowing pipe, only upwards or horizontal, which perhaps is the cause of it failing.

Firing back up the FTC controller then failed in error code EE, comms failure with outdoor unit. Checked all wiring, all seems fine. Did many power cycles to no avail. Eventually re enabled the flow sensor dip switch 2-8, and it boots right up. But now I'm back to the L9 error whenever it tries to do any work. 

It's four years since install.