Megaflow CL120 Backflow issue.

[Tom41]

Hi,

Hi wonder if anyone could help?

I have a customer that has recently had backflow problems with her cylinder. She gets very hot water coming through her cold taps in her 3 floored property. I recently changed her ground floor basin taps and in doing so had to drain down the cylinder as a ball-a-fix valve started leaking circled in yellow. Since completing that job she has had very hot water flowing through the cold taps for 30 odd seconds before going to cold. Obviously this isn't convenient and I am concerned with potential legionella risk.

I believe it could be a faulty non-return valve just after the balanced cold feeds and before the cylinder in photo circled blue.

I you could get back to me that would be much appreciated.

Kind regards,

Tom.

 

[Tom41]

I done some digging and found an installation schematic online. It does show an EV but after the balanced cold feeds?

Edit: I've drawn out a current diagram of the system.

 

[John.g]

That shows the balanced cold taken off before another combined NRV and expansion relief valve but don't see a EV connection, the expansion relief valve is correct.
Going back to your photos, it shows a PRV (pressure relief valve) on the EV with the waste pipe and the inlet/outlet but can't see where this is teed into the system, it might be after the NRV, you can check that out as its not clear to me from the photos, I wouldn't be too worried about the EV as its not a safety device but the expansion relief valve is another matter, if this is required by the regulations then it should be relocated.

This is a fairly good schematic of another UV.

 

[Tom41]

So I can't really recall where in the system the EV is located but I think judging from another photo I have it tops the pressure up on the CH before the primary pump. I've added a photo. Hope this coveys well?

 

[John.g]

Ah, now its clear, that EV has nothing to do with the UV cylinder, its for the CH system, the bubble takes care of the UV expansion, if the pressure is only showing ~ 1.5bar then definitely for the CH.

 

[Tom41]

Ah, now its clear, that EV has nothing to do with the UV cylinder, its for the CH system, the bubble takes care of the UV expansion.

Do you think its worth fitting an external EV anyway for the UV cylinder?

 

[John.g]

No, the UV cylinder volume is fixed so if the bubble is restored properly then its fine, sometimes the internal diaphragm breaks up leading to frequent recharging of the bubble, I can't think of any other reason for a external EV.

 

[Tom41]

No, the UV cylinder volume is fixed so if the bubble is restored properly then its fine, sometimes the internal diaphragm breaks up leading to frequent recharging of the bubble, I can't think of any other reason for a external EV.

Ok, I may have to recharge the bubble then? So with the backflow issue do you think its just a case of replacing that NRV? Also the customer gets very bad limescale was thinking of fitting an electrolytic inline scale reducer too.

 

[John.g]

Yes, I would just replace the NRV and restore the bubble exactly as shown.

 

[Tom41]

Yes, I would just replace the NRV and restore the bubble exactly as shown.

Ok, Thanks John & Rtplumb