New heat exchanger left me with no hot water

[Howard123]

I did indeed. That was one of my first thoughts.

 

[DP]

Next course of action would be overhaul the flow manifold with appropriate Biasi/ Ideal bush and diaphragm

 

[DP]

Such a simple fault yet it is confounding the poster. Basic stuff.

Getting remote guidance is one thing, getting someone who knows what the issue ( I have said either air in the system ingressed during plate HE replacement or pump weak or capacitor goosed) will not create sufficient differential to positively push the flow spindle. This has been checked and established ie spindle moves but not enough to activate the switch due to poor differential pressure during hot water demand. Have had this fault and cured it on this make and others.

My interest post suggestion is to get feed back so I get to know if what I am suggesting is rubbish or kosher. Not helping that the poster has gone AWOL

 

[DP]

Huge thanks to @ianmcd - you are a real star and I cannot thank you enough for all your help and time with this. I tested the diverter valve and it appears to be working. I also tested the flow switch sensor with a magnetic screwdriver and that also seems fine. Sadly still no HW on demand.
@DP thank you for your suggestions - I did as you suggested and although I had to turn the HW on and off several times to be sure, the spindle does indeed come out very, very slightly (but obviously not sufficiently). The air vent is an auto air vent but there is indeed a cap on the top which I have loosened a little. What would you suggest I do to get the air out?

Drop the pressure using PRV though that itself could have detrimental issues. Refill system. If that does not work, seek professional help from someone who knows what he is going ie not a boiler changer but a repairer.
Feedback would be most appreciated as it helps those that have come to your aid be it the fault is stuck in deep mud at the moment.

 

[Howard123]

@DP thank you for following up. I haven't abandoned the post (nor the problem) but being back into the working week means I have very little time to work on this. I will update you as soon as I have anything worth saying but for now all I can tell you is that the problem is still there and I hope to look at it again later today or possibly tomorrow.
Thank you all again for all your help and advice - it genuinely is really, really appreciated.

 

[Agile]

OP, can I assume that you did NOT remove the pump and particularly not the black plastic part behind it?

 

[ianmcd]

Such a simple fault yet it is confounding the poster. Basic stuff.

Getting remote guidance is one thing, getting someone who knows what the issue ( I have said either air in the system ingressed during plate HE replacement or pump weak or capacitor goosed) will not create sufficient differential to positively push the flow spindle. This has been checked and established ie spindle moves but not enough to activate the switch due to poor differential pressure during hot water demand. Have had this fault and cured it on this make and others.

My interest post suggestion is to get feed back so I get to know if what I am suggesting is rubbish or kosher. Not helping that the poster has gone AWOL

CH works fine so pump is fine , it is a restriction somewhere in the Hydraulics when only HW is demanded

 

[Howard123]

@Agile No, I have not removed the pump at any stage.

 

[DP]

CH works fine so pump is fine , it is a restriction somewhere in the Hydraulics when only HW is demanded

No doubt Ian, you are most likely correct, the thing is I had the same fault on the same boiler, it was the pump that was running slow

 

[Howard123]

Quick update - I was fortunate enough to secure some help from an old friend of mine who visited earlier today. I'm not sure I understand how this has worked but he tells me he has replaced the diaphragm and the problem has been resolved.
I'm at a loss as to how it was working fine for CH but not for DHW but I'm looking forward to hot water when I get home from work.

 

[DP]

Covered that at #47

Thank you for the feedback.

The way I see it, right from the start I said pump differential
During CH differential is healthy so spindle rockets out
During HW, differential is just sufficient to move the spindle full distance to operate the switch.

Weak pump may not do it, air in system same issue, spindle gland binding on the spindle same effect ( had that on Monday On a Vokera Linea). Third party diaphragms often ail to prove during hot water demand. All this often heating ok but hot water an issue.

Looking back, heat exchanger that you took out, muck in the primary side equates to better differential so spindle has no problem reaching the switch.

 

[Howard123]

Just to confirm, it's all working a treat.
Thank you all once again for all your help and advice. It is really appreciated.