Header Tank Gunge

[nemo]

Header Tank Gunge

Our central heating system has a separate header tank for the heating side of the system. I had a look in said tank and found to my horror that its has loads of slimy gunge floating in it and more stuff on the bottom of the tank. I'm concerned it could easily block the outlet so I intend to clean out the tank and check that the output pipe is clear.

Q:

1) How does one prevent this gunge accumulating again in the future? The system has always had corrosion inhibitor added BTW.

2) The output pipe is a few cm above the bottom of the tank but there's no filter or other mechanism to reduce the risk of blockage - is there a suitable device to help?

3) The ballcock arm has been set to give only about 6cm of water depth in the tank. Is this setting OK?

[Ian Jackson]

In message , TheChief writes

It was only yesterday that I cleaned out my CH header tank. I took the opportunity because I'm just about to have a towel rail and a radiator replaced, and the system will have to be partially drained.

It's years since I last cleaned it out, and there was a fair amount of soft brown sludge on the bottom, plus a hard-ish thin brown coating on the upper walls. There was also a sort-of thin oily film on the surface. [It gets this way after a few years of neglect.]

To allow for the system to feed the expanded (hot) water back to the tank, the water level is set fairly low (around 5"). This means that there is no reason why it should (normally) ever reach the overflow level.

There is no stop valve in the outlet pipe, so I found a tapered champagne cork that was a perfect fit to block it up. Tying up the float valve when required, I stirred up the sludge and took a stiff brush to the harder coating, and repeatedly drained the tank by siphoning the water off through a long hosepipe poked through the overflow pipe, and going down to the ground level in back garden.

When the plumbing work is done, and the system is being refilled, I have a tin of inhibitor (similar to Fernox) to bleed in to the outlet pipe as things are filling up.

[nemo]

Update ======

Thanks for the advice guys.

I tackled the job today (yeccch). Tied up the ballcock arm then used a small plastic tub as a baler/scraper to clean out the tank. There was about a third of a bucket of gloopy gunge. The outlet pipe connector was hidden in gunge, so presumably at least partially blocked.

I checked that the outlet pipe was clear by slackening the connection to the stop tap in the airing cupboard - clean water flowed.

[John Rumm]

A well fitting lid helps - but its difficult to keep completely gunge free. Inhibitor is one thing. Occasional flushing is about the only other thing you can do.

Make sure the system does not "pump over" as this allows extra air into the system which increases the accumulation of corrosion by products and also algae and mould growth.

The height difference is designed to ensure any sediment is below the pipe.

Remember its also an expansion tank, so at times the level will be higher than the ballcock level.

[nemo]

I'll check it periodically in future.

Don't think that's happening, but I'll watch out for it.

In this case the sediment was deeper and so covered the pipe outlet. Possibly 20 years worth of accumulated grot.

I'm somewhat peeved because the feed pipe has actually become blocked a couple of times, starving the system of water[1] and eventually preventing the boiler from firing up. Each event was sorted and the pipe cleared by plumbers who failed to clear the gunge in the tank, nor even point out the source of the problem - presumably hoping for a repeat job sometime later.

[1] Yes, probably a slow leak somewhere but I can't find it.

Good point - I've left the level as-is.