Can't get my central heating to refill

I fitted a replacement pump and moved a radiator in the bathroom. To do this I had to drain the system.

The new pump is running but I seem to have air locks and it will not draw the water down from the header tank in the roof. Any suggestions. I moved the little lever on the 3 way valve o the manual position rather than leave it in the default auto position. Any other ideas?

the pump is not for drawing down the water from the header tank ?!

u need to turn boiler off at the electrics.

let the system fill up by gravity !!

bleed all rads.

bleed any pipe in airing cupboard with a bleed valve on it (if u find one)
bleed the pump by unscrewing the screw and letting out any air.
now turn the boiler back on and ask for hot water and central heating.

hopefully u will hear aload of air move about and it will sort it self out...if not post again

Do search on blocked cold feed

I tried the bleeding of every radiator but because the pipe from the header tank down to the system may be blocked there was no hiss at the bleeders. I thought it might be an airlock rather than a blocked pipe so I applied mains pressure to the drain off point and opened each radiator bleed in turn. I got a lot of water in but did not completely move the air lock when it started to pour out of the header tank overflow so I stopped. I then tried to bleed more air out hoping that the full header tank might send down some water but no the water seems stuck in the header tank and nothing much in the air seems to bleed out.

If the header tank fills up due to the fact I applied mains pressure to the drain off does that mean that the pipe to the header tank is now cleared? If so why does the head of water not cause the rads to bleed now?

I took the chance and switched on the boiler and it will run for a minute and the pump does run and get hot but I think that is due to friction in the pump rather than hot water from the boiler.

Tried running the hot water circuit only but not yet sure if this is working properly and heating or just pumping cold water. Think it is the latter.

I read a few posts on a blocked cold water feed but they confused me a bit but helped with my general appreciation.

Tried several times to vent the pump but nothing comes out, no air and no water. Do I remove the scew completely or just slacken it 2 turns?

I have checked to make sure that the valves on either side of the pump are open and they are but it seems the pump may not be passing water. It is brand new and is turning and sounds as if it is pumping OK

What should I do now? I have closed everything down as I am on the second floor of a flat and don't want to flood out downstairs during the night.

There are 2 air vents at the boiler and I unscrewed the red caps but I think they may be gunged up. There is a third air vent in the airing cupboard and it too may be gunged up. One possibility may be to replace these as they are twenty years old. What do you think?

Still sounds more like a blocked cold feed than anything else.

What happens if you shut off the mains and, while looking in the header tank have someone open the central heating drain cock?

You ought to see the header tank empty - if it doesn't then you have a standard rust/magnetite blockage. The way to remove it is to cut the cold feed pipe just before it enters the circulating primary water, and poke about to free the T of debris.

You almost certainly have a blocked cold feed, as previously mentioned.

One temporary workaround is to backfill the system using a hose stuffed up the open vent over the header tank. You will still need to manually open the 3PV and bleed the radiators.

You should be able to get enough water in the system to get it to work for a short while.

You will still need to fix the problem permanently though.

The best way forward is to cut out replace the blocked pipework as chances are that the pipe in between the cold feed and open vent is also blocked.

Yes guys everything you say seems to fit the facts as I see them. This feed pipe has been blocked before as there are rust marks on the wall and there is a short 2 inch long insert of new pipe just before the tee which is on the large 22mm? pipe just below the pump.

The insert has been made using 2 of these plastic straight connectors which I think you can remove by pulling back the collar.

Also rather than replace just 2 inches of the horizontal portion of the feed is it better to cut out say 2 or 3 ft of the vertical feed pipe as well to ensure the gunge all goes?

Can you outline how I do this because if I just empty the header tank the vertical pipe will still contain an awful lot of water and this pipe is only 2 inches above the floor in the airing cupboard. Its also a bit awkward to reach. Do I buy 2 new plastic connectors to ensure the repair is the same length or do I use compression couplings that I am used to?

I wondered if I could freeze the mains feed from the header tank say a foot above where I am cutting in. I presume I also have to drain the system again or the water in the radiators will flow out of the primary from the other end of where I cut in. As I am working only a couple of inches above the floor it seems unlikely I could freeze the primary as well. I would be freezing very close to where I am doing my new connection. I have never done any pipe freezing before but it must be straightforward enough

Water will not flow down from the pump because I could close the service valve.

chris547 said:

Yes guys everything you say seems to fit the facts as I see them. This feed pipe has been blocked before as there are rust marks on the wall and there is a short 2 inch long insert of new pipe just before the tee which is on the large 22mm? pipe just below the pump.

Click to expand...

Aha - now we're getting somewhere

chris547 said:

The insert has been made using 2 of these plastic straight connectors which I think you can remove by pulling back the collar.

Click to expand...

Just out of curiosity, is it one of these or one of these?

chris547 said:

Also rather than replace just 2 inches of the horizontal portion of the feed is it better to cut out say 2 or 3 ft of the vertical feed pipe as well to ensure the gunge all goes?

Click to expand...

I wouldn't - the gunge is generally in and close to the T.

chris547 said:

Can you outline how I do this because if I just empty the header tank the vertical pipe will still contain an awful lot of water and this pipe is only 2 inches above the floor in the airing cupboard. Its also a bit awkward to reach. Do I buy 2 new plastic connectors to ensure the repair is the same length or do I use compression couplings that I am used to?

Click to expand...

1. Drain the system.
2. Empty the F&E using either wetvac or sponge and bucket.
3. Put a big towel under the blocked pipe.
4. Demount the plastic coupling.

chris547 said:

I wondered if I could freeze the mains feed from the header tank say a foot above where I am cutting in. I presume I also have to drain the system again or the water in the radiators will flow out of the primary from the other end of where I cut in. As I am working only a couple of inches above the floor it seems unlikely I could freeze the primary as well. I would be freezing very close to where I am doing my new connection. I have never done any pipe freezing before but it must be straightforward enough.

Click to expand...

Far more trouble and expense than simply draining down. And you might get it wrong and lose control anyway.

chris547 said:

Water will not flow down from the pump because I could close the service valve.

Click to expand...

When you say service valve, do you mean the gate valves that isolate the pump? If so, don't rely on those because they're generally hopeless, although you might reduce the flow to a trickle would be enough for to do complete the pipe clearance duties

Looking closely it is more like the grey connector and it is only one fitting not 2 as I said. It is white in colour and does not have any ribs which is why I think you can release it by pulling back. As it is in an awkward place I can send you a digital photo before I proceed so you have proper info. If it could be removed and replaced by a similar fitting it would make the job as easy as it can be in a tight place.

I fully understand the principals of what you advice on methodology and your advice sounds good to me. My mind is clear and focussed!

Main thing is to get the correct fitting before I proceed. I will take my camera to the merchants as well so they can give me the correct bit. I also can check the overall length of the existing coupling using a pair of callipers.

It will take a few towels but I can take my time releasing the water and not just yank out the old coupling.

chris547 said:

Looking closely it is more like the grey connector and it is only one fitting not 2 as I said. It is white in colour and does not have any ribs which is why I think you can release it by pulling back.

Click to expand...

In that case it sounds more like a John Guest fitting of the 'old' variety, which aren't sold anymore.

You will have a little difficulty pushing back the white collar (that releases the pipe) at the same time as pulling the pipe out. Do the collar pushing with a wrench or open-ended spanner or similar, and with perseverence you'll manage it.

Since there's evidence that there's been a blockage here before, then, unless space makes it impossible, I would replace the T. Feel free to post a photo if you want help deciding about this. Of course, if you replace the T then you can just cut out the old push-fit fitting without having to dismantle it.

If you're keeping the T, there's still no need to replace the fitting with an identical one. Although I haven't measured, I'm confident that difference in displacement (of the copper pipe) between different brands of push-fit couplings is negligable.

Don't measure things with too much accuracy, because the cold feed from the loft will have some play in it - even if clipped it will move 1 or 2 mm; many installations have much more.

I sent a couple of pics (low res) to admin but not sure if they will forward them to you. If not I would need your email address or something.

chris547

Chris's Pictures:

Picture 1

and

Picture 2

Ther is another option. It wouldn't always work, but whenever I've tried it, it has. Basically make connections in the loft to push mains DOWN the feed pipe, which sends muck back up the vent pipe which ends over the f/e tank. If you have a stop cock on the f/e supply, all it takes is a long tap connector. One end screws on the tap compression end (1/2"bsp male), and the other (compression fitting end) is right for the f/e tank connector. You can make long tap connectors simply by unscrewing the compression nut and screwing them together. Watch out for sharp ends though which can cut the washer in the tc cap.
Just remember to cap off the tank connector, otherwise the goo you collect from the vent pipe just comes out... You can carry the f/e tank out with goo collected inside.

Usually it's jelly like, thick enough to hang in the pipe by itself. Once it's shifted, you can use chemicals to help get rid of the rest, or at least drain the pipes properly - having run the system to keep you warm while you think about it.

If your connection to the drain cock was really good, and you put a Speedfit cap on the end of the Vent, the mains would push the goo up the feed pipe into the f/e tank. I've never tried that, basically because it needs spare people holding and watching things. It would , again, help a fair bit if it worked though.

That is a very attractive alternative as I have already flooded out my downstairs neighbour when the washing machine waste and trap got blocked with the white/grey cementy stuff.

I have the option to try your idea first and then if it did not work then I can try cutting into the cold feed pipe and physical degunge! Cutting is is still attractive as you know the crap is out!

I am going to ask admin to post another photo (No. 3) as there may be some design issues which mean I must cut in anyway.

Really grateful to everyone as I am gaining an understanding of how the damn system works. I live in North London (Stanmore) and many of the Tradesmen are **** but of course some (the minority) are excellent. How do you find the keepers? This DIYnot site and Forum has been of real value to me, Thank you guys

I am taking this steadily and remember the old adage, measure twice and cut once!

A few words to describe the photo no 3. The pump flow direction is vertically up to the 3-port MZV.

The pumping direction is definitely vertically upwards on the old and new pumps.


There is a 15mm circuit with an auto air valve on the pipe coming out of the top of the 3 port MZV. The 22mm pipe is connected into the HWC about a third up from the base. So presumably the air valve gets air out of the hot water circuit.

The lower left hand 22mm pipe leaving the HWC goes under the floor . It has this 15mm bypass pipe which is connected in immediately above the pump. What does this do?

On the right hand side of the HWC there is another 22mm pipe at the bottom and it has a drain off point. This right hand pipe also is taken up into the roof space and turned back over the cold water storage tank.

The down pointing pipe from the MZV has a 90 degree bend and goes behind the HWC before going below the floor. I assume this is the hot feed to the radiators.

Just recapping, on the input side to the pump closest is the 22mm vent terminating over the F/E tank, just below is the 15mm cold feew which we all suspect is chockers with gunge.

On the output of the pump, there is a 15mm bypass to the lower HWC 22mm pipe, then above this is the 22mm pipe feeding the 3 port MZV.

Comments please