Unvented cylinder system - repair?

[hy288]

Thanks, thats how I thought it was.
Assuming that the E.Vessel is OK and that the E.valve is not leaking but is only dripping when the pressure reaches 6.0bar then the only logical explaination is that the PRV is passing, the cylinder will have to reach ~ 4.7bar (cold) then the expansion will increase that pressure to 6.0 bar to lift the E.valve, the PRV will have to leak past ~ 4.8 Litres to achieve this which is not a lot over a period of time.
You can do a few tests yourself to prove this.
With heating off, Run off say 100L of hot water from a hot tap, then immediately shut off the cold feed to the cylinder and only then shut off the hot tap.
Start heating the cylinder, if no dripping from the E.valve after 20 minutes or so then the PRV, is the culprit IMO.

sorry that info just overloaded me
not wanting to pretending i fully understood this....

 

[hy288]

If it is only dripping when the hot water is being warmed then it has to be an expansion issue, if the vessel's been checked then it can only be the pressure relief valve (PRV), their springs can get softer over time.

If it was the pressure reducing valve (control group) then it would be over pressurising all the time and it would drip all the time, and that's only if your mains is above ~ 3.5bar.

As suggested, loosen the nut on the pressure relief valve and stick a tub under it, fire up the hot water and see if the valve does let by, if so then you need a new PRV.

When you mention that it can only be the pressure relief valve.....are you referring to this expansion valve or PRV valve (6bar) that's built into this combination water valve?
OR are you referring specifically to the temperature/pressure relief valve (10bar) attached to the hot water cylinder?

Regarding the springs on the valves...the system is 8-9years old. None of the valves have been replaced since.

Might be completely wrong, but got the impression if i got discharge from the temperature/pressure relief valve attach to the cylinder, that the discharge would likely be hot water?

During the discharge, i can hear a hissing noise from the combination valve.
As the discharge is either cold or barely lukewarm during the time it discharges...would guess its coming from the expansion valve or PRV valve (6 bar) i.e. the combination water valve.

The engineer has advised me that the next possible action is to get the combination valve replaced.

 

[Johntheo5]

The expansion valve is the safety valve that's Set to 6bar in the combination group, as suggested can you remove the pipe that goes from this to the tundish to confirm or otherwise that it's this valve that is dripping on cylinder heat up.

 

[hy288]

The expansion valve is the safety valve that's Set to 6bar in the combination group, as suggested can you remove the pipe that goes from this to the tundish to confirm or otherwise that it's this valve that is dripping on cylinder heat up.

Thanks. So coming back to my original posted question.
It does sound like that the correct course of action is to replace the expansion safety valve (6bar one) on this combination group.

As the expansion valve is suppose to be available as an individual cartridge. Finding this isn't easy, but did manage to find the exact combination valve that contains this expansion safety valve. Hence, the plan is to simply replace the entire combination valve. Part was about £60, but figured with the age of the existing part we might as well just replace the combined part.

Can you advise if the quote £90+vat is reasonable cost on labour to replace this?
Does the entire cylinder need to be drained to replace? or perhaps partial drained as it sits ~3/4 of the height of the cylinder.

 

[Johntheo5]

Not G3 qualified but that price seems OK. He/She will know what needs draining, fully or otherwise.

 

[ianmcd]

Recently we notice an issue with water dripping via the tundish suggesting a fault. This only happens when the hot water scheduler comes on

Then you circle a box saying it is continuall, cant be both

 

[robinbanks]

@ianmcd I think that post is an exact repeat of yesterday@3:22pm

 

[ianmcd]

@ianmcd I think that post is an exact repeat of yesterday@3:22pm

Then speak to the Mods , I can assure you I didnt get up at that time to send you a repeat post

 

[hy288]

Hi,
Just a quick update. I ended up getting the entire group valve replace (i.e. group valve - pressure reducing valve, expansion valve, check valve etc). Unfortunately it did not fix my issue and we still getting water via the tundish as the hot water heats up.

In the meantime, having considered that we have replaced a new group valve, can I confirm based on my symptoms of cold/room temp water dripping/running slowly down the tundish shortly after the heating of the hot water cylinder.

Can this now ONLY be the case of either a
1) a faulty expansion vessel OR
2) possibly a faulty TPR valve attached to the unvented cylinder?

I'm still awaiting for my engineer to come back to review; and confirm for certainty that the drip is not from the TPR in which case we'll look to get that replaced as the next step. We replaced the group valve as a hissing noise was coming from this when the tundish leak occurred (assuming that it was the in-built expansion valve that was passing water via tundish and perhaps at fault).

I know that previously we had the expansion vessel checked i.e. turned off the inlet main flow, drained and took the pressure off the system, then checked the expansion vessel pressures (topping up to ~3.5bar).
Even though this was done, I assume there is still the chance that the expansion vessel maybe faulty? Or is that nonsense?

In the event that we rule out the expansion vessel, TPR and the group valve.
Can there be other aspects that could cause this cold water leak in the tundish when the hot water cylinder heats up? Or is it the case this again is not possible and can only be one of those components - expansion vessel, TPR or the expansion relief valve on the group valve.

Thanks

 

[Johntheo5]

Can you, as requested previously, remove the pipe that goes from the 6bar expansin valve to the tundish, this will then leave the relief port on that expansion valve exposed to view, you can then positively confirm (or not) that it is this (6bar) relief valve thats lifting when the cylinder commences heating.

 

[Johntheo5]

There doesn't seem to be a balanced cold taken off your valve set, like the example below, so even though a remote possibility, its possible that the cold mains supply to other users, including thermostatic mixer valves is passing over through one of these if faulty ie a shower TMV and pressurizing the system back through the HW cylinder hot take off, this woudl mean a very high mains pressure of ~ 5 to 6 bar with no PRV (pressure reducing valve) on this supply.

 

[hy288]

Can you, as requested previously, remove the pipe that goes from the 6bar expansin valve to the tundish, this will then leave the relief port on that expansion valve exposed to view, you can then positively confirm (or not) that it is this (6bar) relief valve thats lifting when the cylinder commences heating.

I have just had confirmation that the discharge is from the expansion valve from the group inlet.
Its not from the TPR valve.
My engineer has now change his tune and advised me that the expansion vessel is faulty (i.e. no air).
In one hand i'm pleased to know that this is the route cause, but on the other i feel he's let me down in that the servicing did not pick this problem up (in fact i was told the vessel was fine, and they topped it up by 3.5 bar). Hence suggested that the expansion valve may be faulty and require replacement.

Fortunately he replaced this vessel about 3 yrs ago (aquasystem) which i believe has a 5 yr warranty. Now we wait for the replacement. There is still a question on who pays for the re-fitting etc.
Anyways one step forward.

 

[polesapart]

Rough and ready test for expansion vessel:
Shut off water to cylinder, place bucket under bath hot tap. Open hotbath tap, does water come out and then stop?
How much in the bucket? How does that compare to the badged size of expansion vessel (often 18l.)

Edit: I now see the EV was checked.

 

[Johntheo5]

I would confirm the above myself.
If you can, just remove the plastic cap from the top of the E.vessel and press the schrader valve pin with your finger nail or whatever, if air comes out of if nothing (no pressure) comes out then the diaphragm is not ruptured and the EV may just need air end recharging PROPERLY with the water level below the compression nut on the EV pipe, this should be slackened or removed to confirm same and the air end should be pumped with this still removed.
As a start your engineer should do the above FOC and if the EV looses air and lifts the expansion valve, in a short period of say two months or so then replace the EV.
What are the volumes of the HW cylinder and the EV??.

 

[hy288]

I would confirm the above myself.
If you can, just remove the plastic cap from the top of the E.vessel and press the schrader valve pin with your finger nail or whatever, if air comes out of if nothing (no pressure) comes out then the diaphragm is not ruptured and the EV may just need air end recharging PROPERLY with the water level below the compression nut on the EV pipe, this should be slackened or removed to confirm same and the air end should be pumped with this still removed.
As a start your engineer should do the above FOC and if the EV looses air and lifts the expansion valve, in a short period of say two months or so then replace the EV.
What are the volumes of the HW cylinder and the EV??.

We had the HW Cylinder and EV serviced back in Jan. Gave me the impression that the EV was fine, it was just under 3bar and he topped things back up to the pre-charged 3.5bar or there abouts.
The EV is a 24litre Aquasystem. And the HW cylinder is a 250Litre.
At the time of the service, I already notified him that we had an issue with water in the tundish, and figured the service may resolve things (if the EV is just below charge).

Unfortunately, after the service my leaking tundish was not resolved. So the next suggested fix was the expansion valve. Fast forward a few weeks time, we now got the group inlet replaced (containing the expansion valve) and leaking tundish is still happening.
After now reviewing things again, i'm told that the EV has failed. There is no air despite topping things up back in Jan. Hence the suggestion now is to get the EV replaced.
I'm not sure if there is any point in re-topping it up if we did that during the service and now has lost charge.

I guess the issue is that they did not check the EV properly during the service. So abit of bum steer in getting the inlet group valve replaced when in fact it was properly not necessary (as was not faulty since the route cause is likely the EV).
The faulty EV makes sense in terms of my symptoms i.e. leaking cold water in the tundish when the hot water heats up.

Would you say its fair for him to give me a discount on the labour for the replacement of the EV...based on the event as described?