Hot water tap runs dry.

[terrysharp]

I have moved my cold water storage tank and re-routed the hot water pipe running across the centre of my loft, so that I could leave the central area clear and it could be boarded out.

After the job was done I was left with one problem. If I run the hot water taps too fast, air is dragged into the hot water pipe from the safety vent pipe that goes to the cold water storage tank and the hot water flow stops.I then have to back fill the hot water pipe using the mixer tape on the bath, to get the water flowing again.

My question is should I extend the vent pipe down so that it goes into the water in the cold water storage tank and hence cannot drag air in to the pipe but could presumably drag cold water in, or do i do what someone else told me and fit an anti gravity valve to the end of the vent pipe so that no air can be drawn in. If I use the anti gravity valve, would it still allow hot water to exit into the cold water storage tank in the event of an over heating situation in the hot water cylinder.

 

[gas4you]

You must not put any form of valve on the open vent. This is your safety device

It sounds as though there is a pipe work configuration problem, or the tank is not filling fast enough to cope with the outflow from the tap.

Do you have any form of pump fitted to your domestic hot taps?

 

[hi-spec plumbing heating]

My question is should I extend the vent pipe down so that it goes into the water in the cold water storage tank and hence cannot drag air in to the pipe but could presumably drag cold water in, or do i do what someone else told me and fit an anti gravity valve to the end of the vent pipe so that no air can be drawn in. If I use the anti gravity valve, would it still allow hot water to exit into the cold water storage tank in the event of an over heating situation in the hot water cylinder.

i surpose it take's all kinds.
what you don't know don't touch. nearly wet myself muppet

 

[holty]

seems to me like a typical airlock that can be a pain in the backside

 

[chrishutt]

As gas4you put it, a pipe work configuration problem. Perhaps the pipe that you have used to extend the supply from the feed tank is undersized or has air locks in it. It should have at least a very slight rise towards the feed tank.

 

[terrysharp]

Thanks to all for their replies.Even Hi-Spec.

gas4you. No there isn't a pump on the hot water system.

The hot water circuit runs like this. Cold water storage tank in the loft (which is now 18 inches lower down after I moved it out towards the eves), from there new 22mm pipe around loft space and down 1 floor to hot water cylinder. From cylinder back up to loft, around the outside of the loft space in new 22mm pipe,then down on the opposite side of the loft to 1st floor bathroom and ground floor.A 22mm to 15mm T is fitted on this pipe for the vent to the top of the cold water storage tank.

Why the hot water pipe was originally routed back up to the loft after coming out of the cylinder is a mystery to me.

As I said in my original post, the vent pipe does not go into the water in the top of the cold water storage tank. would extending it into the water help my problem and if so by how much would in need to go under the water.

Thanks to all in advance.

I know im a bit of a muppet but i didn't actually fit the anti gravity valve.

 

[holty]

well i think we can rule pipe work configuration as the problem.

 

[terrysharp]

Anymore advice would be helpful.

Thanks.

 

[sambotc]

how high is the point you are running off water in comparison to the level of water in the tank?

You say you've moved th tank lower, maybe you have no head of water now?

Failing that it must be a blockage in either the tank feed to the cylinder, or hot water outlet of the tank.

Sam

 

[Slugbabydotcom]

Failing that it must be a blockage in either the tank feed to the cylinder, or hot water outlet of the tank.

If you haven't opened the gate valve fully on this section of pipe then the 'gate' will effectively create a blockage.

 

[ChrisR]

From cylinder back up to loft, around the outside of the loft space in new 22mm pipe,then down on the opposite side of the loft to 1st floor bathroom and ground floor.A 22mm to 15mm T is fitted on this pipe for the vent to the top of the cold water storage tank.

Sounds all wrong to me.
Could you do a sketch, in Word say?
Save as html and you'll find subdirectory with image files.
Stick one in photobucket and link to it.

Sounds like you're taking water from the vent pipe, which has to be 22mm all the way. DON'T!