Altherma Hydrobox and well water - Heat exchanger corrosion

[Refrigerologist]

I have a client with a less than 3 year old Daikin Altherma installed and the Hydrobox heat exchanger has corroded internally and is leaking refrigerant into the water side.

It isn't one that I installed. Coincidentally, a couple of weeks prior to finding this problem I was speaking to an engineer who works for the company that installed it, he tells me they have had 4 heat exchangers recently that have had to be replaced. They have also had a number of pumps fail.

It is apparent that the system on which I am working is a retrofit on an oil boiler system and no power flushing of the system was undertaken before commissioning the Altherma. I also doubt that any inhibitor has been added to the system

To make matters worse the house is in a rural location and has only well water available from a borehole pump.

I have always added Fernox Protector to the systems I have installed, but I have explained to the client that in his case, simply changing the heat exchanger, then draining down and refilling the system and adding inhibitor may not be sufficient. Judging by the water colour and the magna clean filter the system is full of black iron and sludge.

We carried out a ph test and it was approximately 8.0, which under normal circumstances should be ok. Short of carrying out a full water analysis we are unsure of the water quality coming into the building, although we are aware it does carry silt and particles. The client is going install a filter to the incoming mains water supply. I suggest he speaks to the local company that deals with drilling boreholes for their advice.

If there are any pinholes elsewhere in the system, power flushing may move the sludge that is plugging any holes causing more leaks.

Does anyone have a suggestions as to the best inhibitor to use for well water, which has been drained through the soil and granite below, before being pump back out of the ground?