Lined Radiators?

[thechasman]

Why don't radiators have a corrosion resistant coating inside?

I've seen dozens of posts on all plumbing forums about sludge, pin-holed radiators, oxygen/hydrogen problems, etc. Surely removing a large proportion of the exposed metal surfaces from the systems would solve most of this? With plastic pipes there are only a few things left... valves, pumps, tanks and the boiler. A small dose of inhibitor and job done...

Why are we constantly battling with basic chemistry when we should be ducking the problem with a permanent anti-corrosion coating? Doesn't have to be thick, just inert...

PS If I sound frustrated I paid a fortune for a power flush a few years ago but recently had TRVs fitted and the plumber told me he had to poke his finger through the sludge at the bottom of the radiators.

 

[kbdiy]

PS If I sound frustrated I paid a fortune for a power flush a few years ago but recently had TRVs fitted and the plumber told me he had to poke his finger through the sludge at the bottom of the radiators.

I hope he took the trouble to take them off and flush out the sludge while he was at it.

 

[JohnD]

You obviously have a defect in your system that is causing the corrosion. Perhaps fresh oxygenated water is being added, for example if there is a leak.

Is it an open-vented system with a feed and expansion tank in the loft?

How old is the hot-water cylinder? What colour?

What chemical inhibitor was added after the powerflush?

 

[thechasman]

PS If I sound frustrated I paid a fortune for a power flush a few years ago but recently had TRVs fitted and the plumber told me he had to poke his finger through the sludge at the bottom of the radiators.

I hope he took the trouble to take them off and flush out the sludge while he was at it.

Nope. 16 rads, he was in and out in half a day.

 

[thechasman]

You obviously have a defect in your system that is causing the corrosion. Perhaps fresh oxygenated water is being added, for example if there is a leak.

Is it an open-vented system with a feed and expansion tank in the loft?

Yes

How old is the hot-water cylinder?

20 years

What colour?

Copper with PU Foam coating.


What chemical inhibitor was added after the powerflush?

Whatever BG use.

 

[thechasman]

Not being funny but everyone answered my PS but ignored the question...

 

[JohnD]

that's because radiators do not normally corrode as badly as yours have done. e.g. my old mum's house has rads that were installed in 1970.

What makes them corrode is oxygen in the water. In a sealed system, it is filled up and doesn't change unless you have a leak. In an open vented system, air can dissolve into the water in the feed and expansion tank, and, in small amounts will pass into the water in the radiators. If there is a fault, fresh water may keep being added, or the water may be pumped out of the vent pipe, which speeds corrosion.

You have a particular problem, which must have a particular cause. We are assuming that the powerflush was correctly done.

I will guess that the colour of your cylinder, looking at the insulation, is yellow. You have a feed and expansion tank in the loft. Go and look at it when the system is running. Is there any sign of water coming out of the vent pipe? Is the tank warm? Is the ballcock dripping? How deep is the water? Is there a thick layer of brown silt at the bottom?

It is a very good idea to have a system filter fitted to an open-vented system. It will trap new particles while they are circulating in the water, before they can settle into a blockage, and you can use chemicals to loosen existing sediment so that it gets trapped.

 

[St0rmer66]

Not flushed properly if it was done in half a day with that many radiators. If BG did it then you have a lifetime guarantee as long as you haven't already cancelled your Homecare. Ring up and get them back to do it again. 16 rad's should take more like a day and a half for a first time flush if they were that bad. Downstairs rad's might need taking off the wall, if after the re-flush they're still cold at the bottom when the heating is on then call them back again until it's done to your satisfaction (manager gets involved after 3 visits automatically).

The reason for no coating on the insides of the radiators is a simple one... if you put plastic on the inside for example, then how is the heat going to transfer into the metal of the radiator to actually give the heat off? The job of a radiator is to LOSE heat, not keep it in. Any coating you put on the inside would just be an insulator and stop it heating your room properly!

 

[thechasman]

"If there is a fault, fresh water may keep being added, or the water may be pumped out of the vent pipe, which speeds corrosion."

Thanks, I'll look into that... I'll get an inhibitor test kit and sample once a month to see if it's diluting.

"You have a particular problem, which must have a particular cause. We are assuming that the powerflush was correctly done."

I think that's a rash assumption...

"I will guess that the colour of your cylinder, looking at the insulation, is yellow."

Correct.

"You have a feed and expansion tank in the loft. Go and look at it when the system is running. Is there any sign of water coming out of the vent pipe? Is the tank warm? Is the ballcock dripping? How deep is the water? Is there a thick layer of brown silt at the bottom?"

Will check all of those but need it flushed first... took a rad off yesterday, water is pitch black. Flushing every rad with a hose, running Sentinel X400, draining then refilling. After 20 years of this I really don't trust anyone else to do a proper job.

"It is a very good idea to have a system filter fitted to an open-vented system. It will trap new particles while they are circulating in the water, before they can settle into a blockage, and you can use chemicals to loosen existing sediment so that it gets trapped."

We have one fitted a few years ago but it has been incorrectly fitted upstairs by the hot water tank rather than downstairs on the return... another in the catalogue of errors we have suffered over the years. Last check it was empty so as much use as a chocolate teapot where it is... if the water is this bad it should have been full.

Read more: //www.diynot.com/diy/threads/lined-radiators.413840/#3210203#ixzz3FXpKxoZg

 

[thechasman]

"The reason for no coating on the insides of the radiators is a simple one... if you put plastic on the inside for example, then how is the heat going to transfer into the metal of the radiator to actually give the heat off? The job of a radiator is to LOSE heat, not keep it in. Any coating you put on the inside would just be an insulator and stop it heating your room properly!"

Point taken but I was thinking some sort of electro-plating that wouldn't affect thermal conductivity.

 

[Agile]

The reality is that the only type of coating that could be added is hot dip galvanising.

That would increase the cost of manufacture about three times.

Or even better you could make them out of copper at ten times the cost!

Or stainless steel at forty times the cost.

Rads are basic cheap pressed steel heat emitters made of the cheapest steel which operate for 50 years as long as the system is correctly flushed and designed correctly with no faults.

In the UK we are told to use inhibitors but in most of Europe like Germany the systems are installed correctly and very well cleaned and inhibitors are not normally used.

Heating engineers often see systems 30 years old and with no chemicals added and totally clean water!

Your system has a fault !

Tony

 

[thechasman]

I gave one answer from memory so, naturally, it was wrong.

The hot water tank is green and has a label saying "Grade 4".

Or did you mean the header tank?

 

[thechasman]

"Your system has a fault!"

Agreed.

So...

1) Check ballcock not taking on fresh water all the time.
2) Get water tested periodically for dilution of the rust inhibitor.
3) Check header tank for sediment.
4) ???

We are installing the Aladdin HV30C Autovent bleed valves in all radiators and a similar gizmo in the vent at the top of the hot water tank. They worked flawlessly when we refilled the rads. Cartridge change every 5 years... job done. I figure even if the system is taking on oxygen/air via a leak somewhere at least keeping the rads filled right to the top keeps things as anaerobic as possible.

 

[thechasman]

Okay we've flushed all the upstairs rads. The ones closest to the header/expansion tank, hot water tank and and pump had the most sediment. Fine black stuff in suspension.

The one's at the opposite end of the building were mostly clear apart from one really old one which had flakey black stuff that I think is just age... probably needs replacing.

Does this tell me anything about the probable cause?

Will check header/expansion tank for sediment before we run the system then run it up with X400 added... if that tank gets warm what would that mean? We'll check the overflow/ballcock while we're in there.

 

[doitall]

Ok to answer the original question. if no air can get in then corrosion, sludge etc is non existent, other than residual currents, earth faults etc, and dissimilar metals. O and most fluxes if not flushed after install.

I don't suppose you have a one pipe system by any chance, as this would make any powerflush pointless unless every rad is removed and flushed individually, by the same reasoning it could mean you have the wrong TRVs fitted.