Descaling ASHP heat exchanger

[joth]

- Probably nothing ASHP specific about this question, but I'm specifically asking in relation to an Mitsu ecodan 8.5kW ASHP

- This is the next instalment of my ongoing debacle about flow rate errors, link below. I now know this is not a sensor or plumbing error, but the plate heat exchanger is completely blocked and needing clearing.

 

My plan is to get pickup some Fenox DS3, mix it up with hot water and pour into the PHE. Obviously with the whole lot disconnected from the primary circuit, and using appropriate PPE.

Then flush it all with mains water.

 

If that doesn't clear it up, then I probably need to get Mitsu in to replace it.

 

Interested if anyone has had similar problem and how they attacked it??

 

 

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More background:

1/ original post 2 years ago, thinking it was flow sensor error, then thinking it was kinked flexi pipes.

 

2/ Subsequent update:

I bought a cheap submersible pub (Makita LXT powered) and did some simple flow tests into a bucket:

- without the PHE inline: 35 l/min

- with the PHE inline: 4.5 l/min ---- just a trickle, and critically less than the 5l/min minimum required

 

While flushing it through I initially saw plenty of white-ish sand-like granular dirt come out. Odourless. Presume this is limescale debris:

- We're in a very hard water area; originally (2021) the system was filled (by others) with softened water, but since then I heard that's not advised so on subsequent fills I used mains water and Sentinel X100. It originally had glycol but I've never bothered to refill that. It's been emptied and filled numerous times due to FCU and volumizer additions, as recorded elsewhere on here.

- It has a Fernox TF1 filter, I've regularly cleared and flushed that but never had significant dirt come out - but perhaps a bit of grains of limescale thinking back.

 

My hypothesis now is that this was always the issue, but every time I messed about replacing flexi-pipes and blowing out the airlocks, I was also dislodging a bunch of limescale each time, but it's still had a constant build up that needs to be properly descaled.