Brown Sludge in Feed/Expansion Tank

[Longclough]

I have a question about sludge in F/E Tanks. The reason I am asking is that I have brown sludge build up on the walls of my F/E tank.

Is it normal for sludge to form over time? or is it caused by a system problem?

I am not sure that there is sludge in the system or not. I did drained water out of a couple of radiators and it was clear. Also all radiators heat up top and bottom.

I plan to clean the tank, by draining enough water off to empty the F/E tank, in order to clean it out. Is there any proventative measure I can apply to stop this happening in the future?

 

[JohnD]

it is very common.

don't do as you propose. You shouldn't add sludge from the F&E to the water that circulates through the boiler and radiators. It will cause sediment blockages, gas, and wear out the pump.

Instead, tie up the ball valve and bale or syphon out the water into a bucket. Try to avoid disturbing the mud so it swirls up into the water and gets into the pipe. After baling out as much as you can, sponge the tank clean. You will need to sponge it again using a bucket of clean water. If there is a crust stuck to the sides of the tank you can get it off with a nylon washing-up brush or a green kitchen scourer.

Look at any labels, empty bottles or other evidence of what corrosion-inhibiting chemical has been used before. Sentinel and Fernox are the two best-known and good quality brands. It will usually cost you about £15 for al litre. Add inhibitor to the tank and stir in when you untie the ball to refill it. Fit a lid to keep dirt and dead wildlife out, and fit an insulating jacket to the tank, and foam lagging to any exposed pipes.

If there is no sign that an inhibitor was used, or you don't know which one, best to clean and drain the system and start with a new chemical.

If you have fungus or white jelly in the tank, report back here before doing anything else.

If you get much gas, or black water, out when you bleed your radiators, or if you boiler clonks, bangs or sings when heating up, report back here as you will need a chemical clean.

 

[echoes]

Over how many years has the sludge built up? How old is the tank?
If your water is clear and all your rads are hot top to bottom then it might be just the passage of time.

Rapid sludge build up can be caused by pumping over the vent pipe which aerates the water and causes corrosion - symptom of a blockage or poorly designed pipework.

A leak which is constantly replenished with fresh water would also accelerate sludge build up.

Take a sample of your CH water into a full jam jar with a tight fitting lid and put a nail (un-galvanised) in there and leave it for a week. The nail should not rust if the water is oxygen-free.

If you clean the tank, be careful not to let sludge down the feed pipe - you could introduce a problem you didn't have before.

Is there any proventative [sic] measure I can apply to stop this happening in the future?

Add correct dose of inhibitor to the tank, being careful not flush any loose sludge into your pipes.

 

[Longclough]

JohnD and echoes thanks for your replies.

The system is 8 years old. I have owned the house for 3 yrs.

The previous owner never had the boiler serviced, so I would assume that the tank has been unchecked for 8 years. Is that reasonable time in which this might occur.

I don't have a separate vent pipe, it is a combined feed and vent. How would I determine whether or not it is pumping over?

A leak which is constantly replenished with fresh water would also accelerate sludge build up.

Where exactly do you mean, anywhere in the system.

I have no idea on the history of the system, apart from the last 3 years. I have never added anything to it. Is it best to darin it down fully and then refill adding inhibitor

 

[JohnD]

...I don't have a separate vent pipe, it is a combined feed and vent. How would I determine whether or not it is pumping over?...

In that case it won't be.

If you have no knowledge of previous treatment I would recommend

1) buy a litre of Sentinel X400 cleaner and a litre of Sentinel X100 corrosion inhibitor (they were on sale in Homebase last time I looked, usually about £15/litre). If you are in an area of high limescale and your boiler has been banging, clonking or singing, buy a litre of X200 as well

2) bale out the mud and clean your F&E with the float tied up

3) drain out at least a bucket of water from a radiator drain cock downstairs

4) close the drain cock. Tip the X400 cleaning chemical only into your F&E, untie the ball float and stir to mix well as it is drawn down

5) run the system as normal for 4 weeks. Bleed the rads from time to time and see if the water has gone black (if it does, this is old sediment that has been loosened by the X400)

6) after 4 weeks, drain and rinse a couple of times until water comes out clean. On final fill add the X100 inhibitor and, if you have limescale, the X200. Leave these two in permanently, until you need to drain again, or you might want to top up in 5 years or so. Tie or stick the X100 and X200 labels prominently to the F&E tank or boiler, with date of use.

7) And relax.

 

[echoes]

JohnD and echoes thanks for your replies.
The previous owner never had the boiler serviced, so I would assume that the tank has been unchecked for 8 years. Is that reasonable time in which this might occur.

If he never had a service in 8 years, it might never have had inhibitor checked or added in that time either, so that wouldn't have helped matters.

I don't have a separate vent pipe, it is a combined feed and vent. How would I determine whether or not it is pumping over?

Just watch for any water coming out of the vent pipe, especially when the pump starts and stops.

A leak which is constantly replenished with fresh water would also accelerate sludge build up.

Where exactly do you mean, anywhere in the system.

Yes, anywhere, but I wouldn't worry about that unless you have evidence that there is a leak.

I have no idea on the history of the system, apart from the last 3 years. I have never added anything to it. Is it best to darin it down fully and then refill adding inhibitor

Well if your water's clear, all rads are working well, and the only thing wrong is some sludge in the F&E tank, then I can't really add to JohnD's comprehensive answer.

 

[rojaca]

johnd. what's the white jelly indicative of?

 

[JohnD]

bacterial growth. It is a disgusting slime. If you ever have it, you'll know.