ASHP DHW contaminated

[graham1]

We were away for 4 weeks and when we returned the DOMESTIC HOT WATER was the same greenish colour as water in radiators. After about 3 days the water cleared. Has anybody an idea how the DHW could be contaminated. The pressure in the system remained a little higher that 1. It is an unvented system

[JohnMo]

Cylinder coil or heat exchanger leaking?  It should be the only place where the heat pump fluids and DHW have an interaction.

[joe90]

But if the primary pressure did not drop then there is no leak between the two? 🤔

[Conor]

2 hours ago, joe90 said:

But if the primary pressure did not drop then there is no leak between the two? 🤔

Not if the dhwc pressure is the same or lower than the heating loop. In that case you'd have small fluid transfer from the heating to the water until you got to the point where the pressures equalised. Though I doubt that as you'd normally have higher water pressure than heating system pressure - by nature of the fact that you fill the heating loop with mains pressure water to 1.5bar.

 

@graham1 any idea of the pressure of you mains water?

 

Was the green colour clear (i.e. inhibitor or additive dye) or cloudy / murky (copper corrosion)?

 

 

 

[JohnMo]

Did you have the mains water switched off?

[graham1]

1 hour ago, Conor said:

Not if the dhwc pressure is the same or lower than the heating loop. In that case you'd have small fluid transfer from the heating to the water until you got to the point where the pressures equalised. Though I doubt that as you'd normally have higher water pressure than heating system pressure - by nature of the fact that you fill the heating loop with mains pressure water to 1.5bar.

 

@graham1 any idea of the pressure of you mains water?

 

Was the green colour clear (i.e. inhibitor or additive dye) or cloudy / murky (copper corrosion)?

 

Same appearance as water taken from radiator.  No idea of mains pressure but the shower will almost pin you to the wall!

 

 

[markocosic]

- Something seriously wrong with the plumbing that's essentially connected the mains water to the primary circuit

- Filling loop left connected / open without check valves / with failed check valves

- Failed primary coil in the DHW cylinder

 

Issue may have been there for a while without you realising until you went way for a while or there was a shutdown in the water mains etc that depressurised those whilst you were away.

 

I wonder how many domestic systems (without bright green bitter tasting dyed-and-bittered glycol in them) have failed this way without folks realising? 

[graham1]

Thank you all for your comments.. I /we have np idea what  caused it and I am going to leave things as they are unless it happens again.

Thaks

[joe90]

@graham1 if you need to test can you not drain down your DHW tank and pressurise the heating system and see if the pressure falls (it will fall faster if no water in the DHW tank).