Can plastic cause loss of pressure?

[skenk]

I was in someone's house today and they mentioned that their boiler/ch system (combi boiler) loses pressure occasionally ~once a month or so and needs re-pressurising via the filling loop. The said they had had several folk out to look at their (crappy looking, Alpha? boiler) and the most recent, a BG guy (alarm bells ringing!) told them it was due to them having plastic pipes for their CH (looked like a DIY job). Can simply having plastic pipes cause an intermittent loss of pressure?

I've got a CORGI friend, gonna ask him when I see him next but thought i'd garner your opinions . . .

(i'd have thought it would have to be a problem with the boiler, or a leak but if a leak then it wouldn't be intermittent . . .)

<edit> oops just read the faq alpha boilers not that bad it seems

 

[Softus]

Pipes being plastic can't cause a loss of pressure.

Non-barrier plastic can allow oxygen to leach into the closed system.

Oxygenated water can deplete the effect of a chemical inhibitor.

Unprotected systems can corrode.

Corrosion produces Hydrogen, which compresses and thus lowers the system pressure.

Or there's a leak.

 

[skenk]

Thanks for that

So adding inhibitor might work as a temporary fix but ultimately the whole thing will need re-piped assuming it's non-barrier pipe?

I recall seeing plastic pipe with 'Not for CH' or something printed on it (not in this house but i've seen it) i assume this is the non-barrier pipe that you're talking about?

Would all non-barrier pipe have this or is there another way to find out or standard markings on the pipe? (assuming I can find a long enough length of it to check)

thanks again

 

[WDIK]

Or there's a leak.

 

[skenk]

Fair enough . . . don't think there's a leak at any of the rads, it's been going on so long that someone would have noticed, don't know how many engineers have been out but i would have thought they'd have checked for signs of a leak at the boiler. Could be a leak under the floor but not significant or the downstairs neighbours would have been up complaining.

Is non-barrier plastic usually marked as such?

 

[nickso]

alphas are bad for leaking, particularly around the diverter section.

have the rads been physically checked? i dont mean looking at the floor for pools of water either. each connection actually felt for any signs of water when they are cold, amazing how many times a customer will swear there are no leaks but you then find several by checking properly.

 

[Softus]

So adding inhibitor might work as a temporary fix but ultimately the whole thing will need re-piped assuming it's non-barrier pipe?

If re-piping is too much upheaval and/or too expensive, then you could just re-dose when the concentration of inhibitor drops to below a declared level. You can but concentration testing kits.

I recall seeing plastic pipe with 'Not for CH' or something printed on it (not in this house but i've seen it) i assume this is the non-barrier pipe that you're talking about?

Would all non-barrier pipe have this or is there another way to find out or standard markings on the pipe? (assuming I can find a long enough length of it to check)

Er, can't remember what's on the outside of all the different brands, but barrier pipe has a clearly-seen barrier layer when you look at the cut end of the pipe.

 

[skenk]

Very useful thanks a lot Softus and nickso