Corrosion problem in central heating system with standard plastic piping?

[stevecase51]

Five years ago I had a new central heating system installed. The pipework for two of the radiators was done in plastic, running under the floorboards. Although the system was dosed with plenty of Sentinel X100 inhibitor, after about 18 months the water suddenly started to go brown, and I had to drain the system, flush and refill it, dosing with Sentinel again. The same thing seems to happen every 18 months. The only explanation I can think of is that the plastic pipe used by the installer may not have had an oxygen barrier. The system is operating at about 70 degrees and my theory is that the rate of oxygen intake through the walls of the plastic pipe is such that the Sentinel becomes depleted much more quickly than it would normally. Has anybody else encountered this problem? Also can somebody tell me if it is possible to tell the difference between barrier and non-barrier pipe just by looking at what is printed on the pipe?

 

[ShaunCorbs]

Tbh that’s normal for plastic piping as the fittings arnt barrier and the pipe isn’t 100% air tight

 

[stevecase51]

Tbh that’s normal for plastic piping as the fittings arnt barrier and the pipe isn’t 100% air tight

When you say it's normal, do you mean that having to add inhibitor very regularly is normal with plastic pipes?

 

[ShaunCorbs]

When you say it's normal, do you mean that having to add inhibitor very regularly is normal with plastic pipes?

yep or discoloured water normally around 2 years they need attention

 

[stevecase51]

yep or discoloured water normally around 2 years they need attention

Thanks - so that seems one good reason for sticking to copper?

 

[ShaunCorbs]

Thanks - so that seems one good reason for sticking to copper?

yep or mlcp if you need flexibility (with brass fittings)

 

[EvilDrPorkChop]

It's unusual for Plastic pipe so recent not to be barrier. Have you checked the printed text on the pipework?

I've had a few issues with systems that were done in plastic 15/20+ years ago when the initial pipework wasn't barrier, but nearly all pipework is now from the past 10+ years.

Is it possible Air is getting in somewhere?

 

[stevecase51]

It's unusual for Plastic pipe so recent not to be barrier. Have you checked the printed text on the pipework?

I've had a few issues with systems that were done in plastic 15/20+ years ago when the initial pipework wasn't barrier, but nearly all pipework is now from the past 10+ years.

Is it possible Air is getting in somewhere?

Thanks for that. I plan to check what's printed on the pipe as soon as I can find time to lift the floorboards. I can't think where else air could be getting in. Also I don't have air collecting in the radiators apart from during the first few weeks after draining and re-filling the system.

 

[EvilDrPorkChop]

If it was drawing in oxygen through the pipes i'd expect you to be constantly getting air in the system at the highest point. From my experience of none barrier systems this is what usually happens, or the Auto Airvent lets air out and the system is having to be repressurised regularly.

Your easiest way would be take a valve off and take an insert out to see if there's a barrier.

 

[John.g]

Assuming its a sealed system It might also be worth checking out to see if the system filling valve is set to autofill, this will hide any small leaks but the introduced fresh water will rapidly absorb any inhibitor and lead to corrosion.