Unvented cylinder system - repair?

[Johntheo5]

I assume depressurizing it by turning the stop valve off just below the combo valve...then opening the hot taps to take the pressure off. I believe they did that, and then check the pressure on the EV...topping up appropriately. They did not disconnect the EV physically if thats what you meaning. They did check the pressure of the EV after depressurized, and topped up.

You said you believe they did this originally. if so then the original measured air end pressure of 2.8bar would only result in a final pressure of 4.62bar even if 250L was heated to 60C, the air end pressure could be as low as 1.2bar before the expansion valve would be approaching its lift pressure of 6.0bar again even if heating 250L to 60C, you said the EV was lifting before recharging which it couldn't if the EV was checked as suggested (2.8bar) above so difficult to have any confidence. You should certainly get a discount for labour, I would also suggest that the connecting pipe between the EV and the cold supply to the HW cylinder is removed and proven clear. Also your engineer should check the new EV pressure before mounting it as a small percentage of these have come with no charge and are "flat".

Hopefully not a problem but I would also check out (or get it checked out) the static cold water pressure at a outside tap.

 

[hy288]

You said you believe they did this originally. if so then the original measured air end pressure of 2.8bar would only result in a final pressure of 4.62bar even if 250L was heated to 60C, the air end pressure could be as low as 1.2bar before the expansion valve would be approaching its lift pressure of 6.0bar again even if heating 250L to 60C, you said the EV was lifting before recharging which it couldn't if the EV was checked as suggested (2.8bar) above so difficult to have any confidence. You should certainly get a discount for labour, I would also suggest that the connecting pipe between the EV and the cold supply to the HW cylinder is removed and proven clear. Also your engineer should check the new EV pressure before mounting it as a small percentage of these have come with no charge and are "flat".

Hopefully not a problem but I would also check out (or get it checked out) the static cold water pressure at a outside tap.

So are you saying for me to get the tundish leaks (6bar on expansion valve) then the EV would had to have been as low as 1.2bar? and hence, what we're suggesting is that the original measured air end pressure on the EV of 2.8bar was completely wrong (and likely to be far lower!). Also, when they claimed to top things up to approx 3.5bar that was most likely inaccurate as well. As I continued to get the same cold water tundish leak.
Hence the likely conclusion is that EV pressure measurement/topup and checks were not done correctly. I assume they did not drain the EV properly prior to taking these measures hence were completely off? Would that be the plausible explanation?
Therefore, we ended up misdiagnosing the issue on the potential of a faulty expansion valve on the group inlet when it was likely the case it was working fine and doing its job due to the low air pressure within the EV.

I should add that since they were out yesterday to confirm that water was passing via the expansion valve (not TPR valve). They also rechecked the EV to advise there was an fault/issue with it after all. I know that they tried to top up the pressure again before advising i need a new one.
What I found strange this morning is that there was no leak in the tundish!? It has been leaking consistently for weeks after 10mins once the hot water heats (on morning and night schedule). I am now wondering if yesterday they had topped up the pressure sufficiently to stop the leak. But then again, I can't understand why they've advised the EV was at fault? Should I try pressing the schrader valve on the EV to confirm if air which is as much as i can confidently do.
At the moment, i'm just waiting on their response from their plumbers merchant on the warranty replacement of the EV.

 

[Johntheo5]

Yes, quick reply, will respond in more detail later, just press the schrader pin and check for air, it only takes a few seconds.

 

[hy288]

Yes, quick reply, will respond in more detail later, just press the schrader pin and check for air, it only takes a few seconds.

Hi,
Just tried pressing the schrader pin for air. And i can confirm there's NOTHING!?
This coincide with what the engineer told me yesterday, that there's no pressure.

But I'm now more confused with what is going on now. As I said, this morning i no longer noticed any leaking of cold water via the tundish when the hot water was scheduled to kick in at 7am this morning.
Clearly the EV has no air when pressing the schrader pin (as I have done), so if there's no charge in EV how the heck can the unvented system suddenly stop leaking cold water in the tundish as of this morning?

My initial thoughts of the halt of the tundish leak was because the engineer had re-attempted to re-charge the EV yesterday and perhaps what he told me about the EV being faulty is not entirely true? i.e. the EV is now properly charged and hence the tundish leak is resolved even though he's telling me i need to get a new EV replaced.
But as I have now confirmed there no air when pressing the schrader pin, the engineer is correct. But can't understand why the tundish leak has suddenly stopped?

 

[Johntheo5]

There are only a few possible answers to that.
If the EV is now full of water with the diaphragm pushed up against the air end then effectively there is no EV so the expanded water on cylinder heat up must go somewhere otherwise the expansion valve will lift almost as soon as the heating commences. if we assume heating at least 125L then the expansion is 2.03L or 4.06L if 250L reheated, it doesn't really matter as this water must be "leaking" somewhere, unlikely that its leaking back through the the valve set with its non return valve so most likely its via the hot outlet, either a leaking HW tap or back into the cold mains through a faulty mixer or thermostatic mixer.
Also check that nothing daft like the filling valve is now opened to the flexible hose for topping up the boiler's system red expansion vessel.

Can you post a close up view of the new valve set including where the E.vessel pipe is teed in,

 

[hy288]

There are only a few possible answers to that.
If the EV is now full of water with the diaphragm pushed up against the air end then effectively there is no EV so the expanded water on cylinder heat up must go somewhere otherwise the expansion valve will lift almost as soon as the heating commences. if we assume heating at least 125L then the expansion is 2.03L or 4.06L if 250L reheated, it doesn't really matter as this water must be "leaking" somewhere, unlikely that its leaking back through the the valve set with its non return valve so most likely its via the hot outlet, either a leaking HW tap or back into the cold mains through a faulty mixer or thermostatic mixer.
Also check that nothing daft like the filling valve is now opened to the flexible hose for topping up the boiler's system red expansion vessel.

Can you post a close up view of the new valve set including where the E.vessel pipe is teed in,

No filling valve is closed off to the boiler system - as you can see.
The tundish has been leaking consistently since Jan when i noticed this. Even after fitting the new group valve i was still getting the same cold water leak in the tundish when hot water heats up.
Yesterday they took the pipe work off the TPR and confirmed that the tundish leak was definitely via the group inlet valve; then put things back together. Then the re-checked the EV i.e. turned off the mains inlet to the system, opened hot tap to take pressure off before taking pressure readings on the EV. The mains inlet was turned back on and hot tap running....probably as much that took place.
Was then advised EV is no good, and obviously the cause of the tundish leak.

So very much confused why now the symptoms are different i.e. no leaking in the tundish? I'm certain that whatever actions occurred yesterday has changed something. Will wait and see what happens tonight when the hot water heats during its 7pm-9pm schedule.

Could there be air in the EV but the valve pin is now faulty, hence when i press the pin there's no leakage of air?

 

[Johntheo5]

Obviously the pin may now be faulty but very unlikely IMO, I generally get a very small screwdriver to push it in fully for a second or two, a bit surprising that they didn't pump it up yesterday even as a temporary measure even though its not a safety device and just saves a few litres of lukewarm water every time the cylinder heats up.
The only way that that EV would work to a fashion at 0 bar is if you had pumped it up to any pressure with cyl depressurized and hot taps opened and then released all the air pressure by depressing the schrader pin until all air pressure gone, then restore cyl as was, it would still then not lift the exp. valve unless heating more than 115L, BUT you should get pressure (3.5bar) at the air end as soon as the cold water was restored to the cylinder.
The Valve Set looks a bit unusual to me in that I don't see a port for a balanced take off like the attached, what make is it?.
I suppose see what happens on your heating schedule later on.

 

[hy288]

Obviously the pin may now be faulty but very unlikely IMO, I generally get a very small screwdriver to push it in fully for a second or two, a bit surprising that they didn't pump it up yesterday even as a temporary measure even though its not a safety device and just saves a few litres of lukewarm water every time the cylinder heats up.
The only way that that EV would work to a fashion at 0 bar is if you had pumped it up to any pressure with cyl depressurized and hot taps opened and then released all the air pressure by depressing the schrader pin until all air pressure gone, then restore cyl as was, it would still then not lift the exp. valve unless heating more than 115L, BUT you should get pressure (3.5bar) at the air end as soon as the cold water was restored to the cylinder.
The Valve Set looks a bit unusual to me in that I don't see a port for a balanced take off like the attached, what make is it?.
I suppose see what happens on your heating schedule later on.

View attachment 301286

Originally i tried pushing the pin with my nail without much happening. Then decided to use a chopstick and managed to push the pin in more for a second, but again nothing. Note that the system was still pressurised while doing this.

They did attempt to pump up the EV yesterday. At which point i assume they discovered it was either not hold charge and declared it at fault?

Group inlet is a santon - https://www.unventedcomponentseurop...4661&msclkid=3361dab7832c189188babef780866570

 

[Johntheo5]

40 or 50 pumps from a bicycle pump with system de pressurized would soon tell how long the air is lasting when re pressurized.

 

[hy288]

Obviously the pin may now be faulty but very unlikely IMO, I generally get a very small screwdriver to push it in fully for a second or two, a bit surprising that they didn't pump it up yesterday even as a temporary measure even though its not a safety device and just saves a few litres of lukewarm water every time the cylinder heats up.
The only way that that EV would work to a fashion at 0 bar is if you had pumped it up to any pressure with cyl depressurized and hot taps opened and then released all the air pressure by depressing the schrader pin until all air pressure gone, then restore cyl as was, it would still then not lift the exp. valve unless heating more than 115L, BUT you should get pressure (3.5bar) at the air end as soon as the cold water was restored to the cylinder.
The Valve Set looks a bit unusual to me in that I don't see a port for a balanced take off like the attached, what make is it?.
I suppose see what happens on your heating schedule later on.

View attachment 301286

No sure i followed...
But over the last few days, very different behaviour in the heating schedule.
Its scheduled 7am for 2hrs and 7pm for 2hrs. In the past it's always leaked within 10-20mins of heating.
I've not noticed any leak over the last few days? really odd.

 

[Johntheo5]

It's quite simple, IF there is no air in the air end when pressurised then the expansion is either leaking through the hot end or back through the new combination valve.

 

[hy288]

It's quite simple, IF there is no air in the air end when pressurised then the expansion is either leaking through the hot end or back through the new combination valve.

Seems a bit intermittent but certainly this morning and last night (i.e. 7am / 7pm hot water schedule) water passed via the tundish as before (cold) through the new combination valve.
Not sure why previous days it didn't do that.

 

[Johntheo5]

If somebody draws off even say 1.5/2lL from a HW tap during this period then you won't get the exp valve lifting.

 

[hy288]

If somebody draws off even say 1.5/2lL from a HW tap during this period then you won't get the exp valve lifting.

Just an update - Finally I think we're sorted.
We got the EV replaced, and since then things have been stable. There's not been any water leaking via the tundish. So in the end it looks like it was the EV all along.
Thanks for your advice and info...