Brown stringy muck in CH header tank

[Lower]

I've been moving pipework and replacing radiators room by room over the last few years so the central heating has been drained and refilled quite a few times.

Last time i drained down (and i always turn of the rads so that i don't lose all their water and inhibitor) i dosed the system with sentinal corrosion inhibitor to top up its corrosion resistance.

I happened to look in the header tank approx 6 months after i dosed the system and there is a load of brown, stringy muck in the tank.

So far it appears to only be in the tank so i can clean it out but why has it appeared and what can i do to prevent it happening again?

 

[JohnD]

It is fungal growth. Bale out the tank, clean it thoroughly (and the lid) and remove any dead wildlife. You may find muddy sediment at the bottom, sponge this clean. You can use Kitchen Cleaner with Bleach, as long as you wipe it all off afterwards so it does not get into the radiators.

Adjust the ball float of the filling valve so there is only a couple of inches water depth above the outlet pipe in the bottom (you do not need more. This provides extra room for expansion, and reduces dilution of chemicals)

After untying the ball float so the F&E can refill, add half a bottle of Fernox AF-10 Universal Biocide. You may have to order it from your local plumbers merchant. It is something like £20 a bottle. Keep the other half for future use. The growth may return.

If you are adding system cleaners or corrosion inhibitors, do all that before you add the AF10. The idea is to have it concentrated in the F&E where the trouble is, and it is quite expensive so you don't want to waste it. Look for any signs that the system is pumping over (water coming out of vent pipe bent over the top of F&E).
If the F&E does not already have an insulating jacket, buy and fit one. This stops it getting too warm in summer which encourages fungal growth.

Obviously if the tank does not have a close-fitting lid to keep out dirt and wildlife, buy and fit one.

 

[Lower]

The system does pump over occasionally, primarily because a couple of radiators have been added on a 15mm loop so the pump has to be on speed 2 in order for those rads to get hot.

Is that an issue? It has been suggested that i could block off the over flow to prevent the pumping over as the system is still vented through the feed off the header tank.

Weird thing is that the fungal problem has not happened before. It has only started happening in the last 6 months.

 

[JohnD]

balance the rads better

if it is pumping over, describe or photograph the positions of the F&E pipe and the Vent pipe where they join the circulating pipes

you mustn't block the vent which protects you among other things from the system exploding in case of overheating

What sort of cleaner did you use when adding the new rads?

 

[Lower]

I'm guessing you might have just hit the nail on the head with your last comment.

I didn't use any cleaner when i fitted the last new radiator. I just fitted it, filled the system and added some corrosion inhibitor.

 

[JohnD]

It sounds like quite an old, open-vented sysyem, so it is pretty sure to have sediment. It may have constrictions or partial blockages. This can cause pumping over as well as poor circulation and uneven radiator heating. I recommend you put some Sentinel X400 in it (1 litre will do a typical house at 1%) and run it for 4 weeks. If the circulating water turns jet black with loosened sludge, you will know it is working. If you can afford an extra £100 and do DIY plumbing, fit a Magnaclean as well and I guarantee you will be amazed and delighted at how much it collects.

After you have cleaned it, balance the radiators again and see if it is still pumping over. If it still is, you need to look at the positions of the Vent and F&E joints relative to each other and to the pump.

Clean the F&E out first, but if I were you I would not tip the AF10 in until after you have finished the clean and drain (this is just because of cost).

 

[Lower]

It is an oldish system (approx 20 years) though the boiler is newer than that.

When i first drained the system down there was a lot of black muck in there, but its been drained and flushed over 10 times, all the rads with the exception of one have been replaced along with much of the pipework and when i drain it now there is very little sediment that comes out.

All the rads and the pipework i've replaced have been pretty sediment free. The pumping over is very occasional but i thought was more likely be down to the extension on the system. The original system was piped in 22mm with 15mm feeds to each rad. But where it was extended to feed another 3 rads the pipe was only run in 15mm.

With the pump on speed 1 the rads on the 15mm extension took a long time to get hot. with the pump on speed 2 and some rebalancing the 3 rads on the 15mm extension now get hot too but there is the very occasional pumping over incident.

I'll clean the tank out as you suggested and look at the feed and expansion pipe and the vent pipe join. If i remember correctly they are bridged together about a foot above the pump and then run straight up to the tank about 15 feet above. The vent pipe does have some sort of air separator on it.

 

[JohnD]

it's good that you have removed the loose sediment.

However, when I was working on my old mum's system, which was very dirty, I drained and flushed it and fitted a Magnaclean. After a few weeks the Magnaclean stopped collecting new sludge, so all the loose stuff was gone. I then added X400 and over the next month I got mugfuls of black sludge off the magnet. the X400 had loosened a lot more than the plain water drains had got out.

Maybe I am wrong, but the cleaner will do nothing but good, and certainly do no harm. It is fairly cheap and easy so worth a go.

If you can show photos of the Vent and the F&E pipe it may help. However if they are bridged together it should not pump over. I hope it is not boiling over?