Central heating won't drain - Brown geletanous substance on surface in header tank.

[JohnDorset]

Hi all,

I'm doing some changes to my central heating system which involve moving two rad tails and have discovered that I cannot drain the system.

All the rads are turned off to minimise the water loss but when I opened the drain valve nothing comes out (well just a trickle).

I checked for blockage at the drain valve and no problem.

I went to the old tail and turned the tap on, and the flow increased but only slightly, so I decided to go and check the header tank.

What I discovered is that the header tank is full indicating a blockage in the feed from the header tank. I also suspect a partial bloackage elsewhere as it won't drain when I turn the rad valve on at the old tails.

What I did discover when I went into the roof is that the header tank had a brown geletanous substance on the surface and it is obvious that if this is in the pipes, then I have a real problem.

The heating was refilled with Furnox inhibitor when the main hot water system was upgraded professionally to a non-vented system a couple of years back.


Any clues about what this substance is and how I get rid of it. Call in an expert to flush out the system is an acceptable solution, and that is what I am minded to do, but I would like to know what this substance is and how difficult it is going to be to flush the system out.

Kindest regards

John

 

[dontknowitall]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

Best way is to scoop it out before it can enter the pipework. Some inevitably will travel but a wet vac or ice cream container, sponge and bucket will sort you out. Not an enjoyable job but not all plumbing's just sweet water.

 

[JohnDorset]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

Investigation moved on a little, but not very far.

Remember I have two old tails in the bathroom.

One local plumber said it would be blocked between the header tank and the heating circuit, but that doesn't explain why I can't vent the system when I open the valve on the old FEED tail in the bathroom.

What I have now discovered is that the feed from the header tank is not blocked as I can drain off the header tank through the OUTLET valve on the redundant outlet tail in the bathroom. Opening these valves does not vent the system and allow me to drain the pipework.

I have provisionally arranged for a local plumber to power flush the system tomorrow afternoon and, to be honest, the age of the system is such that flushing is probably not a bad idea. however, it wouyld be useful if I could easily drain the system before he arrives, as this will allow me to fit the new tails before he fills the flushed system.

I don't believe the problem is with the main circuit as the system worked Ok last night and I am coming to the conclusion that the blockage may just be in the drain tail.

I have stuffed a stick up it, but that didn't have any effect. I am however wondering whether or not I might be able to fix it by back flushing the drain vent. If I do I will connect an old washing machine pipe from the bathroom tail to the sink to provide an outlet other than the header tank and thereby avoid the the risk of a flood in the loft if the overflow cannot cope with the flow rate.

Any comments

 

[GQuigley67]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

the substance you mention is sludge/iron oxide/magnetite, it is basically formed due to corrosion of the system(radiators are a ferrous metal so they rust, where as copper/brass are non-ferrous metals which do not rust) Open vented systems are notorious for this as air can enter the system and once it mixes with water starts corroding the system.

a powerflush of your system will cure your problems, i would advise you wait until the plumber arrives as trying to drain it can be risky, i've had to disconnect a pump before and drain with my wet vac, its a messy job though

 

[JohnDorset]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

Thanks GQuigley,

I had a quick go at back flushing it using a hose pipe to the drain tap and a washing machine hose from the tail to the sink as an outlet, but that didn't clear it so I guess I'll have to wait until the plumber arrives to powerflush it tomorrow afternoon.

Pity though that I can't drain it as it would have been nice to have fitted the new tails before the system is flushed.

At least I now know what the problem is and that the solution recommended by the first local plumber I spoke to (which was to cut away the pipe between the header and the system and take it into the garden and flush it) is not a proper solution and can take comfort from the fact that the flushed system will be more efficient and filled with softened water.

 

[stevetheplumber]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

sounds like a blocked cold feed to me hope the flusher links cold feed and vent

 

[JohnDorset]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

I think I actually have done something daft.

Does this make sense. (No need to be polite, "no you daft bat it doesn't" is an entirely acceptable answer).

On all previous occasions when I have drained the system, it has been when I wished to change a rad and the rad I wished to change has been left on which allowed the sytem to vent.

Today, because I just wished to drain the pipework so that I could solder new tails, I turned all the rads off. What I have now discovered is that I can drain the header tank through the old Inlet (hot) feed in the bathroom. I also believe that if I turn on the outlet valve of a least one of the other rads when I open the bleed valve it drains to the outside.

So I'm thinking that the various circuits rely on at least one rad, in the circuit being on (in other words the outlet pipework from the last rad in each circuit simply goes back to the previous rad rather than and there is not a sort of uninterrptable ring ifor the feed and return).

If I'm correct and not talking through the wrong orrifice, then having now manage to get everything dry and soldered the new tails, all I need to do is to clear up the sludge in the header tank and fill the system.

Please tell me I'm not engaging in wishful thinking.

Kindest regards

John

 

[fuzzy]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

sounds like blocked feed, check the tee where it enter main system

 

[GQuigley67]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

have you got a wet and dry vaccum ?? you can try sucking out the gunk from the F&E tank cold feed, clear some of the blockage then refill system with heavy duty sludge remover let your heating run for at least a few hours and then dump again refiling with inhibitor.

be warned you can get airlocks doing this and may get a bit tricky, if your not confident in doing it get a plumber out, your system may be really contaminated and require a powerflush to improve the performance of your heating system

 

[JohnDorset]

Re: Central heating won't drain - Brown geletanous substance on surface in header ta

Many thanks everyone, I think it is all fixed.

I discovered that the drain problem was simply that the cold feed is in the return side of the circuit and the external drain is in the hot feed side of the circuit.

As I had all the radiators and the two old tails turned off the system was not venting when I opened the external drain as it was isolated from the header tank.

I suppose that, in theory, it could have vented through the boiler but I'm guessing the pump / diverter valve prevented this happening. (I have a professionally installed non-vented / pumped hot water system and a vented central heating system with seperate cold feed / expansion connections to the header tank - I did have a common cold feed/ expasion connection to the hearer tank, but that was changed a couple of years ago when the non-vented HW system was installed simply to bring it up to the latest standards.)

I emptied/cleaned all the sludge from the header tank using a bucket and sponge (not a nice job), drained the system, soldered the new rad tails in the bathroom and then refilled the system.

All seems to be operating well.

As I said yesterday, I think I just confused myself when I couldn't drain the pipes with all the rads turned off.

At the moment the new chrome tails are temporarily terminated with soldered end cap bleeds and when I come to the end of the bathroom project the system will need to be drained so that I can remove these and fit the towel ladder/rad. At this time, given that I did have this sludge in my header tank, I will probably follow your advice and flush the system with a heavy duty sludge remover.

Hopefully I won't have problems with airlocks when I flush the system as we have automatic air vents fitted around the boiler and at the heating coil of the HW cylinder.

Many thanks for all your help


John