Kingspan Tribune XE cylinder, air gap needs frequent replenishment

[Postik]

I have a Kingspan Tribune XE hot water cylinder that for the most part works well, but I've had various issues with it including leaking pipework in the airing cupboard and dripping from the tundish occasionally.

In the end I had all the pipework in the airing cupboard taken apart and put back together and that's been fine since.

Prior to this the tundish was dripping and the plumber replaced the pressure relief valve. I am guessing he drained down the whole cylinder when he did this.

Fast forward 6 months and the tundish was dripping again. The plumber showed me how to replenish the built-in expansion vessel but said he suspected the vessel's baffle is leaking because ordinarily you'd expect to replenish the air gap every 1-2 years, not every 6 months.

Now fast forward 4 months and the tundish is dripping again. I've replenished the air gap myself this time and all is well again. But I am concerned it should not need doing this frequently. I can actually tell when the tundish is dripping or about to drip because after the hot water has been on for a while, the kitchen tap is slightly stiffer to turn on. I also suspect this is what caused the weeping pipework before I had it redone (it's a newbuild so the pipework was screwed together as part of a kit, by someone who probably wanted to get home early).

I'm now considering just making it regular maintenance to replenish the air gap every 3 months even if the tunish isn't dripping, but wondered if there's anything else I should look into. The cost of a new cylinder is pretty expensive given this one works okay 99% of the time.

The plumber said what's going on is not typical or normal and he suspects the vessel is faulty. But he also seemed fairly relaxed about me just continuing to recharge the air gap.

Thanks

 

[Johntheo5]

I have a Kingspan Tribune XE hot water cylinder that for the most part works well, but I've had various issues with it including leaking pipework in the airing cupboard and dripping from the tundish occasionally.

In the end I had all the pipework in the airing cupboard taken apart and put back together and that's been fine since.

Prior to this the tundish was dripping and the plumber replaced the pressure relief valve. I am guessing he drained down the whole cylinder when he did this.

Fast forward 6 months and the tundish was dripping again. The plumber showed me how to replenish the built-in expansion vessel but said he suspected the vessel's baffle is leaking because ordinarily you'd expect to replenish the air gap every 1-2 years, not every 6 months.

Now fast forward 4 months and the tundish is dripping again. I've replenished the air gap myself this time and all is well again. But I am concerned it should not need doing this frequently. I can actually tell when the tundish is dripping or about to drip because after the hot water has been on for a while, the kitchen tap is slightly stiffer to turn on. I also suspect this is what caused the weeping pipework before I had it redone (it's a newbuild so the pipework was screwed together as part of a kit, by someone who probably wanted to get home early).

I'm now considering just making it regular maintenance to replenish the air gap every 3 months even if the tunish isn't dripping, but wondered if there's anything else I should look into. The cost of a new cylinder is pretty expensive given this one works okay 99% of the time.

The plumber said what's going on is not typical or normal and he suspects the vessel is faulty. But he also seemed fairly relaxed about me just continuing to recharge the air gap.

Thanks

Check with Kingspan but I don't think they will have any problem if you suggest the installation of a external EV (expansion vessel) sized to 10% of the HW cylinder, if precharged to 2.8/3.0bar then it will still only rise to 3.9bar even after a full cylinder reheat to 65C.

 

[Postik]

Check with Kingspan but I don't think they will have any problem if you suggest the installation of a external EV (expansion vessel) sized to 10% of the HW cylinder, if precharged to 2.8/3.0bar then it will still only rise to 3.9bar even after a full cylinder reheat to 65C.

Thanks, I heard you can fit an external ev to Megaflow, didn't know it was possible with Kingspan but would certainly save a fair bit of hassle if possible.

 

[Johntheo5]

I presume this has a baffle which helps to prolong the times between air bubble recharging times, it may be breaking up, I've seen some horror stories re the Megaflos where bits of plastic then block up thermostatic mixers etc.
Oso also have this air bubble and say you can remove the dip pipe to get ~ 20% more HW volume, I wonder if thse cylinders have a baffle and if so, what happens if you remove the dip tube, does it just float about inside?.

 

[Postik]

I presume this has a baffle which helps to prolong the times between air bubble recharging times, it may be breaking up, I've seen some horror stories re the Megaflos where bits of plastic then block up thermostatic mixers etc.
Oso also have this air bubble and say you can remove the dip pipe to get ~ 20% more HW volume, I wonder if thse cylinders have a baffle and if so, what happens if you remove the dip tube, does it just float about inside?.

I think it does have a baffle. The plumber said the same about the baffle breaking up, but I think he said typically you would find flecks of it in your water and all manner of other issues which I don't have, which is what led him to believe it is simply slowly leaking air.

 

[Johntheo5]

I think it does have a baffle. The plumber said the same about the baffle breaking up, but I think he said typically you would find flecks of it in your water and all manner of other issues which I don't have, which is what led him to believe it is simply slowly leaking air.

The MIs state that this has a cold water dip pipe (as well as the hot pipe dip tube) which enables a full drain down when restoring the air bubble, some, like the Megaflo are only drained until the T&PRV starts gurgling, there is a big advantage in doing a full drain down IMO as on say a 200L Tribune this means that there is a 47L bubble (and final hot pressure of only 3.3bar after a full reheat to 65C) the megaflo or the like that's only drained to the T&PRV height will only have a 9L bubble (and final hot pressure of 4.5bar at 65C), the expansion PRV if set to 6bar will lift on both when there is still ~ a 4.5L bubble remaining so the Tribune has to loose/leak 42.5L of air before the expansion PRV lifts but the Megaflo only has to loose 4.5L of air to lift the expansion PRV. Of course its a pain if you are draining down the full vol each time. Its one of the worlds greatest mysteries to me as to why a PG isn't installed on UV cylinders, it would give a timely warning to restore the bubble and prevent unwelcome high pressures, all boilers have one which gives a warning before the PRV lifts, also its required of course to ensure the correct EV recharging pressure (unlike a UV cylinder with a bubble)

 

[Johntheo5]

Apoligies, re above, I think the Tribune XE uses the same procedure as the Megaflo, I must have been looking at the OSO's bubble restoring procedure where, basically, the cylinder is almost fully drained, it is then recharged with the (all) hot taps closed, when fully pressurized air is then vented from the hot taps, but don't see any reason why the same procedure cannot be used for the Tribune.

There may be nothing wrong with your cylinder, there may be a problem with the 3bar PRV, if thats passing, then overnight, if 3.5L has leaked pass the PRV to pressurize the cylinder to 4.5bar then the expansion PRV will lift after a full reheat, I see that the expansion PRV on the Tribune XE is set to 8.0bar, its no wonder your system is feeling the stress, I would have thought a 6.0bar PRV would be more sensible, check out the one on yours that its a 8.0bar.

 

[Postik]

Apoligies, re above, I think the Tribune XE uses the same procedure as the Megaflo, I must have been looking at the OSO's bubble restoring procedure where, basically, the cylinder is almost fully drained, it is then recharged with the (all) hot taps closed, when fully pressurized air is then vented from the hot taps, but don't see any reason why the same procedure cannot be used for the Tribune.

There may be nothing wrong with your cylinder, there may be a problem with the 3bar PRV, if thats passing, then overnight, if 3.5L has leaked pass the PRV to pressurize the cylinder to 4.5bar then the expansion PRV will lift after a full reheat, I see that the expansion PRV on the Tribune XE is set to 8.0bar, its no wonder your system is feeling the stress, I would have thought a 6.0bar PRV would be more sensible, check out the one on yours that its a 8.0bar.

Unfortunately the PRV was the first thing the plumber replaced last year when the tundish was dripping. So I don't think it's the PRV at fault

And if I'm reading the spec correctly on the side of the cylinder, yes the expansion is 8.0 bar.

 

[Johntheo5]

Unfortunately the PRV was the first thing the plumber replaced last year when the tundish was dripping. So I don't think it's the PRV at fault

And if I'm reading the spec correctly on the side of the cylinder, yes the expansion is 8.0 bar.

Is the PRV a "drop tight" type?, if not then even a relatively small leakage combined with the normal depletion of the bubble will result in more frequent recharging.

 

[Postik]

Is the PRV a "drop tight" type?, if not then even a relatively small leakage combined with the normal depletion of the bubble will result in more frequent recharging.

I'm not sure about the PRV, but the plumber described the cylinder as having a "pin hole leak" (speculation, not confirmed)

 

[Johntheo5]

I'm not sure about the PRV, but the plumber described the cylinder as having a "pin hole leak" (speculation, not confirmed)

Look at the make/model of the PRV, a pin hole leak past over time can and will increae the recharge frequency.

 

[Johntheo5]

Except my spread sheet is lying or I am and assuming no HW drawoff for 8 hrs at night then I reckon a 250L cylinder with the PRV set to 3.0bar and leaking in 1L over the 8hrs, 0.13L/hr will lift a 6.0bar exp PRV when there is still over 70% of the air bubble remaining and will lift a 8.0bar exp PRV with 54% of the air bubble remaining, the same would be true if the PRV is set to 3.26bar with no leakage, so no leakage or a properly set PRV maybe means at least double the time between recharges?.

 

[DontHurtTheNoob]

Do you have a shower pump downstream of the cylinder, perhaps? If the pump siggnificantly lowers the pressure in the cylinder, the air bubble expands and air gets into the water stream, leaving less air in the cylinder. When the pump turns off, the air is compressed again but there is less now and not enough to deal with the subsequent thermal expansion.

I once had exactly that issue with a Megaflo when a shower pump was installed between cylinder and shower. Removing the pump fixed it, I had to live without it...

 

[Postik]

Do you have a shower pump downstream of the cylinder, perhaps? If the pump siggnificantly lowers the pressure in the cylinder, the air bubble expands and air gets into the water stream, leaving less air in the cylinder. When the pump turns off, the air is compressed again but there is less now and not enough to deal with the subsequent thermal expansion.

I once had exactly that issue with a Megaflo when a shower pump was installed between cylinder and shower. Removing the pump fixed it, I had to live without it...

I have two thermostatic bar mixer showers but I don't think they have pumps. There is no electrical isolation switch to either which I'm guessing a pump would have.

 

[Johntheo5]

Do you have a shower pump downstream of the cylinder, perhaps? If the pump siggnificantly lowers the pressure in the cylinder, the air bubble expands and air gets into the water stream, leaving less air in the cylinder. When the pump turns off, the air is compressed again but there is less now and not enough to deal with the subsequent thermal expansion.

I once had exactly that issue with a Megaflo when a shower pump was installed between cylinder and shower. Removing the pump fixed it, I had to live without it...

I have two thermostatic bar mixer showers but I don't think they have pumps. There is no electrical isolation switch to either which I'm guessing a pump would have.

Its interesting even though its very unusual to have a shower booster pump installed after the UV, I wonder is that supposed to be treated the same as boosting the cold mains where I think the flowrate is limited to 12.0LPM?, one way or the other, if say you are using both showers together or boosting after the UV then if the cylinder pressure falls to 1.0bar, the water level will fall close to the bottom of the dip tube or where ever its taken off the side of the tribune and mix/leak into the water stream as stated above. I'm assuming that the dip tube extends down to ~ 25% of the cylinder height.