Plumbing in a heat exchanger

[Dman2]

The loop on a combi boiler is to keep the sealed side up to pressure, not the DHW side

 

[Ukjay]

Your obviously not grasping what i am doing.
I am not touching the sealed side of the system or planning to couple mains water up to it.
I am installing a heat exchanger which has 2 parts to it.
1 the side that that the heat is pumped through which will be part of the sealed system
2 the part that cold water will be fed through from the mains which will come out if the other end hot and be fed to the taps.
There will be no connection between the 2 sides other than the transfer of heat from one side to the other

I am grasping what you are saying I think, but your saying your not touching the sealed side - so how are you heating the water in the exchanger if you are not breaking the closed loop to add another HE in?

From what I read - you will feed mains water into the heat exchanger to heat the cold water to feed your tap (Heat Exchanging from the differential of temperatures from the sealed side to the mains side). The tap plumbing is also going to be housing a mixer valve to set the temperature you want from the outlet.

If your new heat exchanger fractures - and they do fracture, you will be in a position whereby you may be forcing contaminated water into the mains water circuit due to the potential higher pressure in the closed loop side - especially when several taps are opened and the pressure drops on the mains side, hence the reason for the check valve, as if someone severs the mains in the street - you can get back syphoning.
Your risk.

 

[Ukjay]

The loop on a combi boiler is to keep the sealed side up to pressure, not the DHW side

I did not say the loop was for the DHW side - the DHW side is not connected in that way?

The closed loop pressure is set by the circuit being fully closed when you close shut off valve on the fill loop after you fill to the designated pressure as set in the MI's (then the fill loop should be removed if you follow the guidance correctly) - thus has no connection to the mains whatsoever.
This then has an expansion tank - pressure relief valve etc to protect the system from over pressurisation and controls the system pressure.

Anyway - its your call, your installation. I only offered some advise from what I have learnt and what the regs say

 

[Dman2]

I did not say the loop was for the DHW side - the DHW side is not connected in that way?

The closed loop pressure is set by the circuit being fully closed when you close shut off valve on the fill loop after you fill to the designated pressure as set in the MI's (then the fill loop should be removed if you follow the guidance correctly) - thus has no connection to the mains whatsoever.
This then has an expansion tank - pressure relief valve etc to protect the system from over pressurisation and controls the system pressure.

Anyway - its your call, your installation. I only offered some advise from what I have learnt and what the regs say

Apologies @Ukjay
Didnt read your reply correctly
A lot of manflu here so not getting a lot of sleep

Appreciate the advice

 

[Ukjay]

Apologies @Ukjay
Didnt read your reply correctly
A lot of manflu here so not getting a lot of sleep

Appreciate the advice

No apologies required Dman - you simply need to decide which way you want to go. Also - you could use the JFDI approach that is mentioned on here a lot and see what happens.
As for sleep - I can only dream about the last time I was able to see more than three hours continuous sleep