Sludge in the feed/expansion tank - how?

[funkydung]

Last saturday i drained down my central heating system in order to clean out the feed and expansion tank. This was recommended in my home survey before i bought the house.

I noticed that there was a lot of sludge in the bottom of the tank - about and inch deep of the stuff! Not the most pleasant stuff to clean out but I bailed out the tank and removed all the sludge. I then rinsed through the entire system before securing the ball valve and bailing out again.

I then poured a litre of Wickes system cleanser into the feed pipe before releasing the ball valve to refill the system.

Having run the system with the pump set to the third most powerful setting for three days i then popped back into the loft to have a look in the feed tank. Yet again the water was dirty and appeared to have sludge deposits in it.

What i can't understand is how it is getting there! Any ideas?

My setup is pretty much as in this diagram: http://www.sjsplumbingservices.co.uk/images/systemdiagram.gif

Any help greatfully appreciated![/url]

 

[Softus]

Well, it's coming up the cold feed pipe or the vent pipe.

If the system is very dirty, then you might have a partial blockage that causes something known as 'pumping over'. This is where the F&E cistern becomes part of the heating circuit, and is a sign of corrosion, and will lead to even more corrosion.

If you run the heating system and put your head in the loft, can you hear/see a trickle from the vent pipe?

If you locate (often in the airing cupboard) the points where the cold feed and vent pipes, and put a magnet on the pipework section between them, is it attracted to the pipe? This test reveals the presence of ferrous deposits inside the pipe. The fastest way of removing them is to renew that section of pipe, preferably renewing the cold feed and vent connections at the same time.

Please be aware that a system containing a lot of brown sludge is already in an advanced state of corrosion. Any remedial work you do now may result in deposits being removed from areas of very thin radiator metal, and could result in radiators leaking. You don't have much choice though, because putting off maintenance is only delaying the inevitable.

 

[funkydung]

If you run the heating system and put your head in the loft, can you hear/see a trickle from the vent pipe?

Nothing from the vent pipe but what look like small bubbles from the feed pipe (not fast bubbling but image the odd small one comes up)

Please be aware that a system containing a lot of brown sludge is already in an advanced state of corrosion.

Yep, that sounds like my system!

Any remedial work you do now may result in deposits being removed from areas of very thin radiator metal, and could result in radiators leaking.

Scary! An additional hassle to throw into the mix is that mine is an 8mm microbore system! So the pipes are already pretty thin. Most of the pipework is burried in the walls and under chipboard floor on the first floor so i cant easily access them to identify a problem. There are no visible leaks on the rads but i know that 'visible' is not conclusive!

You don't have much choice though, because putting off maintenance is only delaying the inevitable.

I'll try the magnet on the pipe idea and see if that tells me what we're both expecting!

Is it feasible to retain the microbore but replace existing exposed pipework where necessary or do you think it's going to be a case of upgrading to 15mm pipe throughout? If thats the case ive no idea how the pipework would run as it will be difficult to lay under the chipboard on the first floor!

Many thanks for your quick response, i look forward to hearing more!

 

[Softus]

If you run the heating system and put your head in the loft, can you hear/see a trickle from the vent pipe?

Nothing from the vent pipe but what look like small bubbles from the feed pipe (not fast bubbling but image the odd small one comes up)

Hm. I would want to eliminate the possibility that the plumbing is wrong, because that can result in the same effect. In the order of flow, the connections on an open vented system should be vent->cold feed->pump, so that the pump can never drag air down the vent.

An additional hassle to throw into the mix is that mine is an 8mm microbore system! So the pipes are already pretty thin.

Don't confuse narrow bore copper with thin steel. Copper in heating systems doesn't wear out as quickly as the rads.

There are no visible leaks on the rads but i know that 'visible' is not conclusive!

If a rad was leaking you'd know about it, because there would be rusty/sh*tty water dripping from a seam.

Is it feasible to retain the microbore but replace existing exposed pipework where necessary or do you think it's going to be a case of upgrading to 15mm pipe throughout?

Microbore doesn't clog up quite as easily as you might imagine, because the water velocity is much higher than in narrowbore (i.e. 15mm).

...ive no idea how the pipework would run as it will be difficult to lay under the chipboard on the first floor!

I would leave the pipework in if it's working, unless you have another reason to lift the flooring.

 

[funkydung]

The plumbing seems right. It certainly is vent > cold feed > pump. Initially i thought the setup was wrong as in most diagrams ive seen the feed goes straight down to the boiler. But then i saw this diagram: http://www.sjsplumbingservices.co.uk/images/systemdiagram.gif which is exactly how ours is setup. Both feed and exapnsion pipes are cold to touch as they enter the loft from the airing cupboard below. This seems right.

The rads - ah yes, i see. It's the rads that are corroded inside. Luckily none of them leak but are gonna be heavily corroded. In this case it it possible to cure or will i need to buy new rads?

I have three rads upstairs without TRVs as they have not been converted from the single entry point valves (unlike the rest of the rads in our house that have flow and retun pipes on the opposite ends of the rads). I was considering having these changed over to make removal of the rads easier for cleaning. So far i've been quoted £450 + vate to change the pipeworks and put TRVs on these three rads. Good price?

Good to know that i wont need to change from the 8mm to 15mm!

So the question is - are corroded rads curable?

Thanks for all your info!

 

[Softus]

Luckily none of them leak but are gonna be heavily corroded. In this case it it possible to cure or will i need to buy new rads?

You can't cure them. They're not hugely expensive if you replace them as they wear out.

So far i've been quoted £450 + vate to change the pipeworks and put TRVs on these three rads. Good price?

I would be happy (from your point of view) to pay that to someone who's competent, but extremely unhappy to pay someone who isn't. It comes down to how you selected your contractor.

So the question is - are corroded rads curable?

No, and it wouldn't be worth it, given the cost of each one.

 

[funkydung]

Interesting. I think i need to replace the valves then so the system at least meets the building regs! It makes sense to replace these three rads at the same time.

Is there a method to test the rads to see if they are corroded on the inside so i know which ones to replace? Or should i just assume they all need replacing and get them all done in one go?

 

[Softus]

Interesting. I think i need to replace the valves then so the system at least meets the building regs! It makes sense to replace these three rads at the same time.

Building Regulations don't require you to change an existing system, unless it's being modified for other reasons.

Is there a method to test the rads to see if they are corroded on the inside so i know which ones to replace?

Yes. If they leak, they're corroded.

Or should i just assume they all need replacing and get them all done in one go?

Only you can weigh up the risk and effect and cost of having a leak while you're not there. Getting new rads buys you peace of mind. If you can afford it now, then do it now, otherwise put it off and hope for the best.

 

[funkydung]

I guess if a rad starts leaking i'll get it done then!

Still no wiser as to the reason sludge is getting into the header tank though. If the vent>feed>pump is arranged in the right way (it is). And the vent isnt venting (its not) then the only way it can be getting up there is by travelling up the feed pipe. But ive no idea how since the pump cant be pumping in reverse!

 

[JohnD]

every day as the system gets hot, it will expand a bit, and push up the F&E. Then when it cools down it will contract and suck down again.

I've heard the expansion is only a pint or so, however the circulating water will be pumping round and picking up loose sediment, when it gets into the F&E it will be motionless so any suspended solids can settle out and will not be disturbed again.

The more air or gas in the rads, the greater will be the expansion when hot.

p.s. it is much sadder when the sediment settles into a hard blockage

 

[funkydung]

Hi John,

every day as the system gets hot, it will expand a bit, and push up the F&E. Then when it cools down it will contract and suck down again.

That makes a lot of sense.

I've heard the expansion is only a pint or so, however the circulating water will be pumping round and picking up loose sediment, when it gets into the F&E it will be motionless so any suspended solids can settle out and will not be disturbed again.

Yes, this seems to be the case. In that respect the F/E tank is acting as a filter, taking sediment away from the flow. This can only be a good thing! I'm happy to bail it out every now and then but 30 years worth was in there on saturday which accounted for about 1 inch! So im not overly worried about it building up quickly!

The more air or gas in the rads, the greater will be the expansion when hot.

Fortunately there is no air in there at the moment. One rad needs occasional bleeding (a few times a year) but im of the opinion that as its a particularly large rad and probably at the highest point, maybe it's corrosion and hydrogen or somesuch in there rather than air..

You've done a lot to put my mind at rest there!

I'm going the leave the concentrate cleanser in the system for a month or so before draining down again to get the three upstairs TRVs installed. I might put another months worth of cleanser in after that too before any inhibitor goes down the pipe!

 

[JohnD]

I'm not familiar with the Wickes cleaner. if you can leave it in for weeks, I presume it is a sediment-loosener that helps it wash around so you can rinse it out. With these it helps to rattle or bang the rads with a rubber hammer, or I've heard you can use a roto-stopped drill on a block of wood, to shake free lumps of sediment. Yoi will spot blocked radiators by the cold patches they have.

There are other, acidic cleaners that are more aggresive and can't be left in for long. If you have rusty old radiators they might be a bit of a risk.

If you find black sediment, a Magnaclean will trap this and is very gratifying to use. But it will not trap brown rust, which is (almost) non-magnetic.

 

[funkydung]

I'm not familiar with the Wickes cleaner. if you can leave it in for weeks, I presume it is a sediment-loosener that helps it wash around so you can rinse it out.

This is the stuff. Its the sort that can be left in the system like sentinel x400. The difference here is that it removes sludge AND scale. I was concerned that i might have some scale to deal with. Nothing founded on fact mind!

With these it helps to rattle or bang the rads with a rubber hammer, or I've heard you can use a roto-stopped drill on a block of wood, to shake free lumps of sediment.

Good tip! i will try. All the rads are working well. All get very hot, very quickly. But im gonna do the rubber hammer thing anyhow for good measure!

There are other, acidic cleaners that are more aggresive and can't be left in for long. If you have rusty old radiators they might be a bit of a risk.

Yeh i saw these cleaners but ive not used them. Fortunately there is no evidence of rust anywhere on the rads nor in the circulating water.

If you find black sediment, a Magnaclean will trap this and is very gratifying to use. But it will not trap brown rust, which is (almost) non-magnetic.

I saw magnaclean on a website earlier. At £100 it looks like a good deal. Maybe that's my next step. I'd need to identify the best place to install it though. How about on the primary flow between the pump and the hot water cylinder? Seems to be space for it there.[/url]

 

[JohnD]

it is suppose to go on a return pipe, then it will catch some stuff before it gets to the boiler and pump. return from rads is better than return from cylinder as cylinder does not rust. best fitted on a 22mm vertical pipe, otherwise it will spill when you unscrew the top.

if you fit one you will be really pleased to see what a lot of sediment it traps.

 

[funkydung]

best fitted on a 22mm vertical pipe, otherwise it will spill when you unscrew the top.

I haven't got much vertical 22mm pipe available to me. The boiler is in a cupboard and access to the return is tight - maybe about 2-3 inches exposed above the cupboard.

Ideally it would go in the airing cupboard somewhere but by the sounds of it that wouldnt be a good idea!

The towel rail in my bathroom is on the primary circuit (not sure if on the flow or return though). I wonder if a bit of clever pipework around here could make space for the magna?

if you fit one you will be really pleased to see what a lot of sediment it traps.

Sounds like a very satisfying device. If only i had somehwere suitable to site it!