Central heating draining (again)

[John Carlyle-Clarke]

I've done some googling, read a lot of old posts, and looked at the FAQ's, but I can't see this particular question answered. I have a sealed system, with a Combi. Most of the CH pipework runs between the ground floor and first floor, i.e. in the ceiling if you are downstairs. The pipes drop down to downstairs radiators, which are on their own or in pairs. Each drop has its own drain tap.

I usually activate the safety vent to depressurise. Then I start with the lowest radiator, by the back door and drain that. I get a lot of water out of that. As it's draining, I open the bleed valves on all the upstairs rads.

Then I do the drain in the bottom of the boiler, and a big rad nearby in the kitchen. As do each downstairs raid or pair, I open the bleed valves in those too. These ones usually drain fine.

My question is that with the remaining 4 drop circuits with their taps, I never seem to be able to get any more than a trickle out of them, if that. It's not enough to run down a hose

- so I have to fiddle with plastic trays. Some of them, nothing comes out at all (although If open the bleed valves, water comes out). Often I've thought they were empty because the tap has stopped running, but when I've removed the rad or undone a pipe, a gush of water comes out.

Am I missing something obvious here? Or are they just bad taps? Dismantling one, I can see how they'd leak, but not how they would not flow. Is there a better way to do this job?

I am seriously considering making something to fit into a radiation plug - possibly out of a spare plug from an old rad - with a fitting to accept a footpump. I'd use this pressurise the system with air. This would serve two purposes - one, before refilling after work, I could pressurise the system and use gas leak detector spray to check joints - two, it would help with draining I think by forcing remaining water out. Is there any mileage in this idea?

Finally - how long can I leave Fernox restorer in the system? I think it's been a couple of weeks now - is that a problem? I'm putting off draining and refilling because it's such a hassle. Also, if I just drain the majority of the system and don't bother with a couple of rads, and refill with inhibitor, will this cause a problem that not all the descaler has been drained/flushed out?

Thanks in advance.

[Haam S lo]

possibly out of a spare

pressurise the system with

could pressurise the

help with draining I think by

Yes, it works well. I connected a cordless electric tyre pump to a radiator bleed valve whilst draining down after a cleanse. I did this because I live in a top floor flat where all of the pipework is under the floor below the drain point which is on a radiator valve. After gravity draining all of the radiators, this pipework is still full of mucky water. Using the pump, I managed to get all of this residual water out, and quite fast too. The pump is a Bosch PAG 12V pump and comes with a black conical attachment that you can manually hold in the radiator bleed valve body to form an air tight seal. It also has a pressure gauge on it so you know when to stop pumping before something blows! If you made a proper seal to the bleed valve and closed the drain valve, you could perform a completely dry leak check by watching the gauge for air pressure losses over time.

[Set Square]

I would expect to be able to drain the water in the 2 drop pipes plus that in the radiator itself without too much difficulty. Are both rad valves fully open? Is there a TRV between the rad and the drain point which could be closed at summer temperatures - blocking the path from the rad to the drain point?

Interesting! In another recent thread about removing radiators to decorate, I posted details of a device which I had made - consisting of a Schrader valve silver-soldered into a bored-out 1/8" BSP fitting to screw into a radiator in place of the bleed assembly. For the thread, see:

watch the wrap!]

If you didn't want to make a fitting, you could use one of Mr Screwfix's Water Pressure Test Gauges (item 10179). This has an attached Scrader valve, allowing the system to be pressurised with air for dry testing and - in your case - evacuation. If you built a stub pipe with isolation valve into your system, you could easily attach this device when required. [You would probably also need an isolation valve in the pipe to the expansion chamber. Otherwise, you'd do a lot of pumping just to pressurise that!]

[John Carlyle-Clarke]

"John Carlyle-Clarke" wrote in news:Xns95796EE3618C8johncceuroplacercouk@192.168.1.69:

It occurs to me that perhaps I could open the filling loop and run water out of each drain tap for a while to flush the additive out. Perhaps I could even drain the easy bit (which would get the boiler storage and the upstairs rads as well as a couple of downstairs ones) and then use the pressure of the filling loop to push the dregs out of the hard to drain bits?

[StealthUK]

couple of weeks

a hassle. Also, if I

refill with

drained/flushed out?

You should have a drain c*ck fitted at the lowest point possible with no need to remove a radiator (unless they are heavily sludged). Have a hose pipe connected to it and out the door. Open all bleed valves starting from the top radiators.

After flushing the system out with cleanser do another 1 or 2 cold fills and flush out again before the final fill with inhibitor. Yes it's a lot of walking about the house with a key and container but won't take that long.

I wouldn't use the safety valve out of the boiler too often to drain as IME they are a bit dodgy and can end up leaking.

[Ed Sirett]

can't see this

CH pipework

downstairs. The pipes

has its own

radiator, by the

open the bleed valves on

kitchen. As do each

drain fine.

seem to be able to

hose - so I have to

open the bleed

stopped

I can see how

out of a spare

pressurise the system with

pressurise the

draining I think by

couple of weeks

a hassle. Also, if I

refill with

drained/flushed out?

CH drain taps are apt to become defective over long periods of time. The rubber (often) or fibre (sometimes) washer tends to stick fast in the tap. As you undo the spindle the 'buttony' peice [1] that spears the washer comes out of the washer and very little water comes out. None if there is a certain amount of debris on the wet side of the washer. These can be quite a trial, since if you remove the spindle completely and then try to dig out the remains of the washer you will get a flood which is OK if the drain point is routed outside over a gully.

In your situation you will have to shut off the rad, drain the rad on its couplings, then drain the pipework as you open the rad valve. When all is clear then you can risk opening up the drain c*ck. Use a fibre washer if possible.

[1] What is its real name? Jumper centre point?