Water tank in loft

HarryS

Hi, I have almost no cold water coming from my mixer taps on the bath. The hot water is fine. The tank also feeds the shower, which is working.

It was working fine before I stupidly left it running for hours and must have drained the tank

I can hear water from the tank, but it is difficult to get to, so I haven't been able to look in the tank ( I am a senior lady)

There is water trickling when the tap is turned on and it is clean

Can anyone suggest what may be wrong please? Thank you in advance

Belenus

It could be an airlock in the pipe feeding the cold water to the bath.

Turn all the taps in the house fully off. Wait a while until the loft tank is full of water. Set the bath temperature mixer to cold and then fully open the tap. Be prepared for lots of gurgling and splashing as a water and air mixture comes out of the tap.

With luck that will clear the airlock. 

If not then you might need to attach a mains pressure hose pipe to the bath tap and force mains water up the mixer tap to clear the airlock. Take further advice on that before proceeding as it is many years since I have had to clear an airlock and I may be mis remembering what I did,

You might be advised to get a handy man or a plumber to do that for you.

Bendy_House

Sounds like a classic case of an air-lock.

When a tank empties, air gets drawn in and down the pipes. If your shower is working fine, then there are two possibilities: One is that the shower cold is supplied by its own pipe from the CWS (cold tank) which is quite possible, but not so common, and the other is that possibility is that the airlock (air bubble) is located in a pipe between where the shower tees off, and the pipe gets to the tap. Quite possibly there's a horizontal section of pipe supplying the cold bath tap, perhaps even with a slight upwards bend or slope in it where the bubble could be sitting.

(Of course, another possibility is that the mixer is faulty, but if it happened when you drained the tank, suspicion must fall there in the first instance.)

How to sort? The usual way is to force water up that mixer in the opposite direction, and this dislodges the air bubble and sends it burping back up to the tank. This requires water at a greater pressure, so you'd need to run a hose from the kitchen cold (at mains pressure) to the bath mixer spout. And then cobble a way of connecting it that won't spray everywhere!

Once you connect the hose at both ends, you first open the mixer tap - making sure the 'cold' position is as open as it can be - then you slowly open the kitchen cold tap, turning it up steadily until it's a pretty much max flow. Let it run for 30 seconds. Shut off the kitchen, and then the bath mixer. Remove the hose from the mixer, open up and see if she flows. If it almost does, but then slows or coughs, repeat, but for a minute (don't be shocked if the tank overflow starts raining water outside).

Is the bath upstairs? If so, another method is to 'suck' the air out. Get a hose as before, connect it to the mixer spout, run the hose downstairs and outside - in as neat a run as possible - and take it to the garden tap. Open the bath mixer cold fully and leave it for a good minute like this just to see if this does the trick - sometime the small water flow will be enough to draw more behind it and out the spout, finally drawing the air bubble with it. If this doesn't work, then connect the outside end to the garden tap, turn it on slowly and not full on (unless the hose pops off...) and let it back-fill the hose for a good 30+ seconds. Whip the end off the garden hose and lay it on the ground - watch to see what happens. The water should pour out with some gusto, and continue doing so by drawing - sucking/syphoning the air bubble out with it.

HarryS

Thank you for the replies. Sounds a bit too much for me personally to deal with. I may have to get a plumber.
I appreciate  your replies though as I will at least have the knowledge 

plumb1_2

Let the hot water go cold, then open the cold tap on the mixer, then place your palm over the outlet and open the hot tap, . There might be just enough pressure to move the air lock?

Otherwise it’s a mains pressure job,

coffeehound

Also, if you happen to own one, a wet and dry vacuum cleaner should be able to pull the airlock through when the hose is attached to the tap’s spout. Works on one repeat offender i know of

Bendy_House

plumb1_2 said:

Let the hot water go cold, then open the cold tap on the mixer, then place your palm over the outlet and open the hot tap, . There might be just enough pressure to move the air lock?

Otherwise it’s a mains pressure job,

Since both the hot and cold are ultimately supplied by the same CWS in the loft, their pressures will be similar at the tap. I don't see this working.

southcoastrgi

Bendy_House said:

plumb1_2 said:

Let the hot water go cold, then open the cold tap on the mixer, then place your palm over the outlet and open the hot tap, . There might be just enough pressure to move the air lock?

Otherwise it’s a mains pressure job,

Since both the hot and cold are ultimately supplied by the same CWS in the loft, their pressures will be similar at the tap. I don't see this working.

I can....

Bendy_House

Explain please!

grumbler

Because of the air in the cold water pipe cold water pressure in the tap is zero (it doesn't flow).

Hot water pressure is normal.

If you close the tap outlet with a palm/finger, hot water will start filling the col water pipe, pushing the air in the pipe up to the tank.

Bendy_House

Hmm, I see a flaw...

Yes, there is no flow, and yes you can imply that - by this - there is no pressure. But what there is, is an effective 'block' caused by the bubble, and beyond this bubble is cold water backed by the same pressure as the hot water at that level.

So, the cold might not be flowing, so the cold might not have a 'pressure', but once you try and push that bubble back up, you will be forcing it against that static pressure - which the hot will not overcome.

Think of it this way - close the cold tap shut! No flow = no pressure at the spout. But on the other side of that tap there is pressure. At the other side of the bubble, there is pressure.

Harry, where is this bath - I'm guessing upstairs if it's not a bungalow? Do you have a hose? Great! Can you figure out a way of attaching it to the mixer's spout so's it's sealed - say by wrapping duct tape around it? Marv.

Ok - idea; this is risk-free Attach the hose (even worth buying a spout adaptor for this), and unravel the hose in as straight a manner as you can downstairs and out the door. Turn on the 'hot' tap only, and let it run until water is coming out solidly from the hose end - no splutters. Ok, now also open the cold tap fully, and then shut off the hot.

I'll bet you a brass monkey that the syphonic flow of water down the hose will easily 'suck' the bubble out the cold pipe and restore flow.