I (think I) blew up my HEP2O DHW flow !!

[Andy Y]

I hope I’m posting this in the correct forum, so here goes:

The attached photo speaks for itself: ‘exploded’ 17-year old 22mm Hep2O barrier! My question is how/ why?

Let me be the first to recognise this may well be a naïve self-inflicted wound but here is the full story in the hopes I can get some constructive feedback/advice:

The pipe in question was the first 150mm of my HW flow immediately after a Grundfos UP 20-45 N 150. The pump duty is set to ‘1’. This was a replacement for an older Grundfos pump which had seized (because it was only very briefly connected and thus hardly ever actually used). The pump was originally fitted to speed delivery of HW to our kitchen sink (and external doggy shower) which is some 25 metres horizontally from our cylinder, a BASI Hydras HY150LIND. The pipe runs consist of a 22mm loop (flow /return) to the BASI and is ‘Tee-d’ onto a 15mm leg that serves the kitchen /doggy shower.

I’m a controls/automation tech so needless to say it took me forever and a day to get around to actually hooking up my own pump! The ‘exploded’ pipe occurred about a month after the pump was connected to the controls and thus regularly run. The controls consist of a flow switch on the return pipe which triggers a timeout-relay such that the pump shuts off automatically after about 12 mins from the initial flow signal. I discussed this with my plumber buddy and we agreed that once hot water was available at the kitchen sink there was little point in wasting power by having the pump continue to run. Of course this also means a short-duration run of the hot tap may well have the pump running after the tap is closed but as the 22mm loop would/should not be restricted by closing the kitchen tap – WHY DID THE HEP SPLIT? J Maybe it’s nothing to do with my control setup and pressure but the pipe was quite happy until the pump was recently put into service.

The BASI cylinder stat is set to 55’. I have just ordered a hot water thermostat so as to verify the actual water temperature that is passing through the pipe. Probably not relevant, but the boiler is a Glowworm 30sxi.

Please let me have your thoughts? Thanks in advance.

 

[townfanjon]

If thats hep its in the wrong fitting , thats a speedfit tee.

 

[Best]

Too much heat will break down the barrier pipe. Just goes like in your photo. But I have no certainty in what has caused that

 

[Andy Y]

If thats hep its in the wrong fitting , thats a speedfit tee.

Thanks, yes it is HEP but the Speedfit 'T' is not really relevant to the question. It has since been changed and the damaged piece of pipe replaced with 22mm copper.

 

[Andy Y]

Too much heat will break down the barrier pipe. Just goes like in your photo. But I have no certainty in what has caused that

Actually, I'm wondering if a combination of 'too hot' water and the environment that the pipe is installed in are the clues. The closet through which the HW flow is routed also contains the UFH manifolds and is regularly around 35'C in winter. Any idea what the external environmental maximum is for HEP2O?

 

[Sharp Point]

Plastic pipe isn’t supposed to be used on a secondary hot water circuit. A secondary hot water circuit should be installed in copper.

 

[ShaunCorbs]

and this is why plastic pipe cant be used on a secondary water pump / circuit

 

[ShaunCorbs]

If thats hep its in the wrong fitting , thats a speedfit tee.

aslong as you use the hep inserts its fine / you can use anyfitting town

 

[Best]

This all then also points to the unvented cylinder install and operation requiring a G3 plumber to check everything.

 

[Andy Y]

and this is why plastic pipe cant be used on a secondary water pump / circuit

Wavin's advisory seems to suggest that Hep2O can be used for DHW but not for CONTINUOUSLY pumped circuits. In my case the pump was typically only running for a matter of minutes per hour - or am I just splitting hairs here? I fully appreciate that real-world experience speaks louder than a sales claim
Actually the difference in hot water delivery time was minimal with or without the pump operating so I'm inclined to just remove it at this point. Thanks for all the input.

 

[ShaunCorbs]

No sorry to say no plastic pipe can be used for a return circuit

And you might need the pump

With the pump off and a valve shut on the pump / return circuit

Leave it for a day / over night with no one running hot water

Go to the furthest outlet away from the cylinder and time the time it takes to get hot

If more than 30 seconds it needs one

 

[townfanjon]

aslong as you use the hep inserts its fine / you can use anyfitting town

Nah , not in jonnys world its not lol

 

[Chuck]

Of course this also means a short-duration run of the hot tap may well have the pump running after the tap is closed but as the 22mm loop would/should not be restricted by closing the kitchen tap – WHY DID THE HEP SPLIT? J Maybe it’s nothing to do with my control setup and pressure but the pipe was quite happy until the pump was recently put into service.

I don't like plastic pipe for permanent installations.

A possible explanation for your failure is that if the kitchen tap shuts rapidly (e.g. a 1/4-turn design) a hydraulic shock wave will propagate back up the pipe and the transient rise in presssure leads to failure of the pipe.

The size of this effect depends on the pipe diameter and flow rate before the tap is shut, but according to

Filtration Water Hammer Calculator

a 3/4" pipe supplying water at 1 gal/min will experience a 19psi transient rise in presure due to hydraulic shock when the tap is suddenly stopped. So, this could plausibly have been the straw that broke the camel's back.

 

[ShaunCorbs]

Nah , not in jonnys world its not lol

 

[townfanjon]

Think about this , you mix some plastic fittings and pipe and flood a house , do you think the insurance will pay out ?? “ I rest my case “ lol

 

[ShaunCorbs]

Think about this , you mix some plastic fittings and pipe and flood a house , do you think the insurance will pay out ?? “ I rest my case “ lol

Speedfit and hep will warrenty there fittings / pipe if on used other manufacturer pipe aslong as the same manufacturer inserts are used

Same could be said for compression fittings

 

[townfanjon]

Speedfit and hep will warrenty there fittings / pipe if on used other manufacturer pipe aslong as the same manufacturer inserts are used

Same could be said for compression fittings

So if there is a leak , which manufacturer does you or the insurance company claim off lol . 50 % each maybe , nah . Never mix them . Its the law !!

 

[johnduffell]

Are people saying they think the non matching fitting is at fault? I feel like the issue was a combination of pressure and temperature over time. Remember at high temperatures the rated pressure of plastic pipe drops off rapidly.
In our install I didn't trust plastic pipe completely as our water meter has a check valve, so I installed one of those mini expansion vessels in the feed. This avoids any overpressure due to quick closing of taps and water warming up ambient temperature.

 

[townfanjon]

Are people saying they think the non matching fitting is at fault? I feel like the issue was a combination of pressure and temperature over time. Remember at high temperatures the rated pressure of plastic pipe drops off rapidly.
In our install I didn't trust plastic pipe completely as our water meter has a check valve, so I installed one of those mini expansion vessels in the feed. This avoids any overpressure due to quick closing of taps and water warming up ambient temperature.

No John , I am not blaming the odd fittings I just commented on them . I never mix fittings .

 

[SimonG]

The fault was caused by incorrect materials on a secondary return.

 

[Ric2013]

In college I was taught that a secondary return pump should be on the return to the cylinder. This actually makes no sense, as I'm not sure how you'd guarantee that you didn't end up dragging in air from the taps and even my teacher was dubious about the claim that putting the pump on the return was the best way. But anyhow.

Hep does indeed say that its product is not suitable for secondary returns, but not why. Given that the same sudden shock from cold to hot would occur in a hot water distributing pipe whether or not a pump is involved, it can't be that. Nor can it, logically, be the temperature involved, as, if suitable for heating (radiator flow at 80°C), then carrying hot water for handwashing at 60°C should be a doddle.

All I can imagine is that Hep is not suited to the potential vacuum created by a pumped return.

Regarding mixing fittings, my feeling is that there is nothing technically wrong with it so long as the correct insert for the pipe is used (though someone I trained under insisted the insert should match the brand of fitting, not the brand of pipe), but I would still not do it as I have been unable to find a manufacturer's document that specifically allows it. My feeling is that although Hepworth/John Guest etc allegedly refuse to accept any liability anyway (local merchant claims they always find some excuse), at least, if it goes wrong, I won't be making myself look totally incompetent by mixing fittings. Based on that, I prefer to use copper in the first place.

 

[johnduffell]

Nor can it, logically, be the temperature involved, as, if suitable for heating (radiator flow at 80°C), then carrying hot water for handwashing at 60°C should be a doddle.

Agree kind of, but Not quite on its own as a heating system just has water sloshing around gently below 3 bar.
Mains hot water could be over 3 bar with shocks from water hammer (perhaps someone mentioned that already) and expansion of water heating up on downstream of an nrv.

 

[Andy Y]

..........

Hep does indeed say that its product is not suitable for secondary returns, but not why. Given that the same sudden shock from cold to hot would occur in a hot water distributing pipe whether or not a pump is involved, it can't be that. Nor can it, logically, be the temperature involved, as, if suitable for heating (radiator flow at 80°C), then carrying hot water for handwashing at 60°C should be a doddle.

All I can imagine is that Hep is not suited to the potential vacuum created by a pumped return.

Indeed - and this is the exact text from the current Hep Installer Guide:

A continuously operated re-circulating system is a water-replenished circulating system which is maintained at a constant
high temperature to provide a constant source of hot water.
Continuously operated re-circulating systems are used to
distribute constant hot water to draw off points that may be
distant from the heat source or hot water storage vessel.
Continuously operated re-circulating systems are very different
from conventional hot water supply and central heating systems
found in domestic properties, for which our products have been
tested to, under either BS 7291 2010 Class S or WRAS approval
standards, and for this reason Hep2O products must NOT be used
on any continuously operated re-circulating systems as they are
not approved under the current version of these standards.

As a couple of other contributors have also pointed out here and in other threads Hep are only stating that their product is "not approved under the current version of these standards".
i.e. it has not been tested accordingly. To my mind this is sloppy wording and having read the guide cover to cover there are also a couple of other examples of sloppy advice.

Clearly in my own experience Hep can fail in such an application. However any material can fail given a combination of adverse circumstances and we can all speculate why failure may occur but it would be so much more informative for Hep to state the practical reasons for limitation of use. Whether the limitation be specific combinations of pressure, water temp, warming/cooling requirement for the material, etc, etc, leaves us all none the wiser!

 

[Ric2013]

Agree kind of, but Not quite on its own as a heating system just has water sloshing around gently below 3 bar.
Mains hot water could be over 3 bar with shocks from water hammer (perhaps someone mentioned that already) and expansion of water heating up on downstream of an nrv.

At 60°C, Hep should be able to take 9 bar. I would accept water hammer or expansion after a NRV as an answer, BUT, this would equally apply to unpumped hot water, which Hep claims its product is suited for. Plot thickens.

 

[ShaunCorbs]

At 60°C, Hep should be able to take 9 bar. I would accept water hammer or expansion after a NRV as an answer, BUT, this would equally apply to unpumped hot water, which Hep claims its product is suited for. Plot thickens.

looks like old non barrier stuff