Grr... CH system and braided hose bother

I’m getting an awful feeling of déjà vu today.
I was round at my mother’s flushing her CH system when she commented that the bathroom radiator/towel rail didn’t get hot.
Having checked that it was full of water and that it wouldn’t get hot even when it was the only radiator switched on in the system I established by bleeding it whilst opening the two valves in turn that there was no flow or continuity through one “leg” of the radiator.
I went under the floor of the flat (easy to do via a basement entrance) and tried to trace the plumbing. With a sinking heart I spotted that a section of braided flexible pipe had been used for a “tricky” connection. It’s almost certainly going to be a bastard to replace as it disappears under the bathroom floor and access is extremely limited.
This’ll be the second time I’ve been cursed with inappropriate use of braided (probably “Speedfit”) hoses in a CH system. The last time was on my Myson kickspace heater.
Lest there is any doubt, these fecking hoses are NOT for use in CH systems! Speedfit website clearly says so. Do not let any plumber fit them in your house.
/end grumble.
Tim
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On 23/01/2018 21:40, Tim+ wrote:

Do they get blocked easily?
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I think the lining swells. Whether it’s just the long term effect of hot water or the effect of corrosion inhibitors I don’t know but the end effect is no flow. When I get the bastarding thing out I’ll cut it open and see.
Tim
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On 24/01/2018 08:22, Tim+ wrote:

I see.
I recently removed some old rads, and they had some very sticky black gloop in. If that's bunging up your hose, you might be able to clear it rather than replace it.

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No cos they then leak which was why my cold tap needed one changing. The lining had split when we tried to bend it a few years after fitting no doubt due to lime scale on the inside of it. Indeed between these and the convoluted so called bendable ones that get pin holes at the flute corners, I've yet to find a flexible pipe with a long life. Brian
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On 24/01/2018 08:22, Tim+ wrote:

One of the problems is that a kink can flatten the tube.
In theory, cheap and nasty nitrile rubber should be OK for quite a long time at central heating temperatures and chemistry.
You *used* to be able to buy flexible corrugated copper tube with a solder fitting at each end, I used one once on an awkward bath.
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In this case though it’s a short 12” straight section. No bends.

Whatever the theory, Speedfit do not recommend their hoses for CH use.

Still readily available.
https://www.screwfix.com/p/flexible-copper-plumbing-stick-15-x-x-300mm/61598
Tim
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On 24/01/2018 13:03, Tim+ wrote:

Similar in stainless from Toolsatan
https://www.toolstation.com/shop/Plumbing/d20/Flexible+Connectors/sd2807/Flexible+Stainless+Steel+Hose/p16172
or
https://tinyurl.com/ybu96vam
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On 24/01/2018 21:57, alan_m wrote:

I thought this was great, and then I read the reviews.
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On 24/01/18 08:10, GB wrote:

IME constsant hot water flow degrades the rubber which breaks down
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On Tuesday, 23 January 2018 21:40:25 UTC, Tim+ wrote:

Oops. Does this apply to only the low temp rated ones or to hot rated ones too?
NT
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I don't like them anyway, I got lacerated fingers trying to get one undone on a cold water tap in a kitchen a couple of years ago. they seem to shred and th sharp ends are like rose thorns. Brian
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On 23/01/2018 21:40, Tim+ wrote:

Speedfit ones may not be, but Myson kickspace heaters defintely used to come with braided flexis - I helped my father fit one about 20 years ago and it is still running fine.
SteveW
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On 24/01/2018 21:20, Steve Walker wrote:

Mine came with braided hoses 18 months ago.
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Be prepared for the heat output to drop to zero then.
Tim
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Touch wood, 15 years since installed and it must still be putting heat out because one of our cats loves to sit in front of it and get a blow dry. Strangely she's scared of hair driers.
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Braided pipe in situ: https://photos.app.goo.gl/JLEQHgNDXWTU1HDg2
Pipe extracted: https://photos.app.goo.gl/SboH9X72KB1E85DJ2
Cross section of middle: https://photos.app.goo.gl/zWlm3bm0E2lUG0mA2
Cross section of end near coupling: https://photos.app.goo.gl/EcNQthYVIhjakL5h2
As expected it was a bit of a bugger to extract but fortunately there was enough access to allow me to use my quickcut on the pipe beyond the inaccessible joint and re-join it all with a longer loop of speedfit tubing and connectors.
When I cut the braided section in two there was thick black gritty sludge completely filling the pipe. It could be displaced by running it under a fast flowing tap though. I then cut through it immediately adjacent to one end and whilst there was a bit a moveable sludge. The end of the pipe was filled with a hard plug of impacted material.
So, it's clearly not the rubber swelling as I imagined but a build up of either corrosion of the fitting itself or deposition of crud in the pipework perhaps exacerbated by small internal bore of the connectors. (About 6mm).
Anyhow, as this is the second time I've seen this happen with these flexible hoses in CH systems I think that it's a strong indication never to use them.
The radiator is now toasty and warm for the first time in years. A very satisfying hour's work.
Tim
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wrote:
<snip>

It all seems strange to me as the last system I worked on was my Mums and that's mostly an ex gravity system and the pipe sizes are huge! ;-)

Or anything that substantially reduces or restricts the flow, especially where it's not easy to access / service.

Excellent.

It's lovely when a plan comes together eh. ;-)
Cheers, T i m
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Actually, I think it’s the flow restriction and probable inadequate corrosion inhibitor that combine to lead to the blockages. I’ve probably been a little unfair to the hoses in that nothing appears to have gone wrong with the rubber and there’s no corrosion of any hose components that I can see.
When you have a 15mm pipe that is constricted to 6mm, then opens up to about 12mm before going through another 6mm constriction, I think you probably have the perfect device to trap any circulating crud.

Indeed. ;-)
Tim
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<snip> >> Or anything that substantially reduces or restricts the flow,

Ok ...

Quite, and whilst the hoses themselves may not have actually failed as such, (as you say) the 'design' seems to be party to there being an issue in the first place?
<snip>
On Mums system the first 'restriction' in the system is the heat exchanger so after some bathroom reworks we felt some scale had broken free (and there wasn't much in general) and was sitting in the heat exchanger. We took it out but it seemed clear enough (considering how old it is) but after putting it all back together it seemed ok again. <shrug>
Cheers, T i m
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