Pex Tubing Rupture

[paulbasel]

Hello everyone, first time here and I hope someone can help me with some information.

In my home I have a hot water heating system powered by a Viessmann Vitodens 333 which is a gas fired condensing boiler. We added an living room extension onto the house 6 years ago and the heating contractor ran PEX tubing to three radiators that are embedded in the floor of the extension. For 6 years the system functioned without a problem.

About 8 months ago we had a leak from the PEX tubing and after opening the floor we saw that it had a 4 cm split in it. The heating contractor who installed the system originally cut it out and spliced a new section into tubing. At the time he claimed that the material failure was due to the weather having been so cold for 2 weeks. I didn't buy the argument because there is hot water circulating through the system at all times, particularly when the temperature is under 0 C.

Now, a leak has developed in different section of tubing in the same extension. They haven't opened it up yet but I'm sure it will be the same problem as with the first leak. Now, the same heating contractor is saying that the temperature from the Viessmann boiler is too hot, i.e., when the boiler must heat water there is a surge in the heating system and this weakens the PEX and therefore causes a leak.

I'm sure you can understand my scepticism. I wish I could tell you more details about the type of tubing but all I have seen is that it is while, about 20 cm in diameter, and has an aluminum lining. By the way, we live in Switzerland if that helps.

My question is, does this type of tubing rupture under normal operating conditions? And, if it does, what are the possible reasons for that happening.

Paul

 

[Charnwood]

does this type of tubing rupture under normal operating conditions?

No. Rare as rocking horse dung.

 

[Agile]

There is some semi rigid tubing I have seen with several layers including aluminium. I would be very surprised if that type split.

The normal plastic as used for plumbing can stand about 6 Bar at temps of 80 C.

BUT the pressure it can stand very rapidly decreases as the temp rises. Perhaps 1 Bar at 115 C.

You dont mention the temp or pressure that you run your system at?

I would wonder if the expansion vessel is faulty and allowing the pressure to rise too high. Do you know if it has ever been checked???

Plastic buried in concrete should virtually never burst because the concrete will withhold bursting. Perhaps the concrete was poor with air gaps around the pipe? Or was it encased in insulation?

Quite interesting!

Tony

 

[RobinClay]

Ask Google. ISTR it's 6 bar at 20 deg C and 3 bar at 90 deg C.

The tubing is called PEX-AL-PEX. Google that, too.

 

[RobinClay]

Just f.y.i., the PlumbSure piece of pipe in my hand is stamped:-

QUAL-PEX
BARRIER PIPE
BS7291 PART 3:2010 CLASS 5
15MM
PE-X
12 BAR 20 DEG C
4 BAR 82 DEG C
3 BAR 92 DEG C
0091310-0155
015M
(ALWAYS USE PIPE INSERTS)
PRD# 123456

... but your pipe is probably different...

 

[Onetap]

My question is, does this type of tubing rupture under normal operating conditions? And, if it does, what are the possible reasons for that happening.

Very unlikely, usually only found after prolonged freezing of the tube.

Does the pressure relief valve (PRV) on your boiler work? There is usually an 'easing lever' or knob that can be operated to open the valve, to check that it moves. It's the only means of testing the operation of the valve, without removing it. They will often fail to reseal after this and then need replacing, but if you've had two or more tubing bursts, it may be the tube is acting as a pressure relief device in the absence of a working PRV.
Replacement PRVs are quite cheap.

PRVs can concrete themselves shut, if there is a slow leak through the valve, usually in hard water areas (maybe not Switzerland).

Check that the PRV discharge pipework is clear and has a continuous fall, i.e not liable to fill with water which could then freeze.

 

[Agile]

freezing of the PRV vent makes the boiler effectively unable to have any protection against excessive presures.

That does not need a vent pipe with any places for water to congregate, all it needs is for a constant srip to freeze like a stalagmite until the whole vent is closed solid.

That may well be the cause of the problem. Most likely to have burst due to excessive pressure when warm than freezing in the concrete.

Tony

 

[RickyLee53]

freezing of the PRV vent makes the boiler effectively unable to have any protection against excessive presures.

That does not need a vent pipe with any places for water to congregate, all it needs is for a constant srip to freeze like a stalagmite until the whole vent is closed solid.

That may well be the cause of the problem. Most likely to have burst due to excessive pressure when warm than freezing in the concrete.

Tony

Stalactite unless it defies gravity.

 

[Agile]

No, stalagmite!

They grow upwards from the floor until the block the entire cavity being wide.

Stalagtites and thin and dont block the cavity!

 

[RobinClay]

[coff, coff]

Just f.y.i.,
StalaGmites come from the Ground, while
StalaCtites hang from the Ceiling..

 

[Dan Robinson]

Stalagmites might grow tall.

Stalagtites hang on tight.


That's how I learnt if when I was a lad

 

[Onetap]

Mites grow up.
Tights come down.

 

[Charnwood]

When the tights (tites) come down I might (mite) go up!

Perhaps our teacher was a bit on the crude, rough-and-ready side.

 

[bolshy]

Anyway, it's called an icicle