Kettling boiler

[ivahunch]

I have added some inhibitor to the CH header tank to help cure kettling and want to ensure it enters the system
So I tried opening the drain valve at the low point (beneath a radiator) but no water comes out
DAK why this is and how to fix it?

[pochisoldi]

Zone valve closed? Try turning off power to the system (to ensure the boiler doesn't kick in) and then moving the lever on the valve to the open position.

[richlist]

My plumber recommends adding a bottle of fabric softener into the heating circuit to fix kettling.

[ivahunch]

Zone valve closed?

The system is very simple and doesn't have a zone valve

[pochisoldi]

Is there anywhere for air to get in so the water at the bottom can get out?
Ensure that all radiators are on (open all thermostatic valves), and then have an assistant open the bleed valve on the highest radiator after you've opened the drain valve.

[TheMotorcycleBoy]

I have added some inhibitor to the CH header tank to help cure kettling and want to ensure it enters the system
So I tried opening the drain valve at the low point (beneath a radiator) but no water comes out
DAK why this is and how to fix it?

Perhaps the sealing washer is stuck against it's seat....try removing the thread part and poke within the bore very gently with a little pick or screwdriver or something. But be prepared for when the water does come out.....

[bungeejumper]

Perhaps the sealing washer is stuck against it's seat....try removing the thread part and poke within the bore very gently with a little pick or screwdriver or something. But be prepared for when the water does come out.....

Indeed, if it's an open vented system (i.e. with a header tank), then there's no reason why it shouldn't release water from the drain valve. (Unless, of course, both the valves on the radiator in question have been closed for some reason.) Stuck washer in the drain valve is the most likely cause.

I'm not sure I'd unscrew the valve core completely until I'd tried just about everything else. You've got more than 100 litres of water in that system, and it's going to take a bit of stopping once it's in full flow. (It will also replenish itself with yet more water as the header tank cistern kicks in. But hey, you've tied up the ball valve in the loft of course?) Some of the radiator water may be filthy black stuff that will ruin your carpets.

Maybe try unwinding the valve by just two or three turns and then tapping it gently? If you're going to risk the torrent, at least make sure you've got something (lump of putty?) that you can ram swiftly into the valve once you've lost the valve core under the kitchen table and the cat is floating away in the direction of the front door.

Kettling is best cured by a specialist treatment such as Sentinel X200, rather than a general purpose system treatment. In most cases the agent will work by itself over a period of a couple of months, even if you don't drain water off. But yes, it's better if you can solve the problem properly. A stuck drain valve is just a booby trap waiting for its next opportunity to spoil your day.

BJ

[TheMotorcycleBoy]

Yes BJ is right. You've got to be careful with black water spoiling stuff. I've done loads of plumbing so I'm pretty gung ho. But I put lots of spare towels down on the floor, and have a contigency plan e.g. a helper (Mel !!) with strong thumbs!

[tjh290633]

Caution when kicking valves. I once kicked a stuck steam trap on a tar tank, which fell off and then released a stream of hot tar, which bounced off an adjacent tank and spattered me from head to foot.

My white lab coat never looked the same again, but the dry cleaners did a good job on my trousers. The rest of me scrubbed up reasonably well. This was in 1958 before H&S had been invented.

TJH

[jfgw]

It is very common (normal, even) for a drain-off cock washer to get stuck. You may need to completely remove the screw and puggle with a screwdriver. Plugging both the feed pipe in the tank and the open vent pipe will reduce the extent of the flood.
Get a replacement washer or two. The old one may not reseal, especially if it breaks up.

Julian F. G. W.

[bungeejumper]

Get a replacement washer or two. The old one may not reseal, especially if it breaks up.

Thanks Julian, I'll put it on my list for the next time I do a complete drain-down, and will do the lot.

Do you happen to know whether washers (and indeed drain valve cores) are universal? The square 'spanner edges' on some of my cores are getting a bit nadgered, due to 50 years' worth of amateurs abusing them with pliers.

Fortunately, all but one of my downstairs drain valves are no more than 25 years old. Most of the upstairs ones look similar but are probably into their sixth decade, and I'm not sure I can be @rsed to unsolder them all.

BJ

[pochisoldi]

A lazy sod workaround might be to pick a radiator located somewhere where a spillage would hurt less, shut the rad valves (noting the number of turns required on the lockshield valve) and then drain the radiator. The worst case spillage will then be whatever the capacity of the radiator. Any further drainage could be done via the disconnected pipe controlled by the radiator valve.

Once the job is done reconnect everything, open the lockshield valve by the same number of turns that it took to shut it, and bleed the radiator.

[stewamax]

Stuck washer! The washers are typically quite small - much smaller than a tap washer.
Wait until the water has cooled.
Put a pan or something absorbent or waterproof under the valve. It won't need to catch much water
Attach a hosepipe to the drain cock and vent the pipe to a suitable drain outside. Use a Jubilee clip to ensure that you don't accidentally knock the hose off the drain cock.
Open the valve slowly. You will probably find you can unscrew it completely and nothing happens, but you see the washer still in place.
Unseat the washer with a small screwdriver.
As soon as water gushes out, put your thumb over the now-open valve. All the water will flow down the hose.
When the flow dies down a bit, quickly replace your thumb by a cork or similar.

[jfgw]

Do you happen to know whether washers (and indeed drain valve cores) are universal? The square 'spanner edges' on some of my cores are getting a bit nadgered, due to 50 years' worth of amateurs abusing them with pliers.

The washers are standard. You may well be lucky swapping cores but they are not universal.

Put a pan or something absorbent or waterproof under the valve. It won't need to catch much water

Some dribble more than others. Type A drain-off cocks have a seal, type B ones do not and always dribble.

Julian F. G. W.