refilled cold water tank ok. No water from taps.

Hi,
I woke this morning to hear drips falling. I located the leak to the valve on the pipe running from the cold water storage tank in the attic. There was a fair bit of limescale on the underside so I think it must have been going a while.

I was unable to stop the leak with either tightening the compression fittings or adding ptfe tape.

Luckily I have not too long ago replaced a manual valve on the bypass with an automatic valve which the boiler instructions recommended. Prior to this the valve worked opened/closed fine but the system was a lot quieter after and I doubt the boiler was getting the required flow. So I had a spare manual 22mm valve.

So I turned off the water supply and drained the cold water tank. Then replaced the valve. I have then turned the water on and the tank has filled to it's old level and is well above the outlet pipes. However there is only a slow trickle of water coming from the cold water taps.

I have double checked that all the valves are open including the new one (which isn't leaking).

The tank is one and a half floors above the cold taps.

I'm guessing there is a blockage in the pipe? Do you think this is sludge (there's not much at the bottom of the cold tank and it doesn't reach as high as the outlet pipe) or is it an air lock?

I've tried blowing water down the outlet pipes but that didn't help. Tapping on the tank outlet pipe seems to slightly increase the flow rate.

I'm just off to buy some fittings to attach a hose to a tap as I've seen reverse filling suggested on another thread. Do you think that's a sensible thing to try?

Thanks in advance for any help you can give!

ps. There are two outlet pipes near the bottom of the cold water tank; I'm not quite sure why.

I'm back already. I connected a garden hose from a sink which is connected to the mains to on in the bathroom and gently opened the tap. When there was a small amount of water running through I ran up to the loft and could hear bubbles. All the bubbles were coming from one of the two pipes near the bottom of the cold water tank.

When all the bubbles had stopped I turned off the tap and after a bit of banging noise the taps all having running water.

Still confused about why there are two pipes leaving the cold water tank at the same level. Not sure where the other one goes to (?hot water tank?).

Still all seems sorted except letting some plaster dry and repainting where is has become discoloured.

Yes, this was undoubtedly an air lock. Not at all uncommon.

The two pipes are for hot and cold. The hot essentially presurises your hot tank so that there is pressure avaible at the taps on the same floor as the tank. It goes to the bottom of the hot tank and the outlet is on top. Hot water rises above cold so there is always the hottest water at the top of the tank.

thanks GJS!

That makes a lot of sense; i guess there's two, rather than one that splits into separate pipes to the taps and tank, so there's no reduction in hot water pressure when the cold tap is turned on?

Exactly. This is sometimes called a balanced system, where the pressure from hot and cold taps will be the same as they are fed from the same tank, thus have the same head.