air in hot water flow: the return

Is there any significant difference in the temperature that the immersion and the boiler heat the cylinder to?

Is the temperature when connected to the boiler controlled by a cylinder thermostat or just the boiler's stat?

yes there is a difference, the immersion was set very high (because of the problems I had getting any water out in the early stages) at about

Sirett wrote:

I've just sketched your system. I think this would explain it:

The water level in the vent pipe will be the same as in the tank. The junction where the hot water Ts off from the vent pipe is not much below the water level when the tank is full. When you run a bath, the level in the tank drops, as does the level in the vent pipe, until it reaches the T, when air stars to get drawn in.

The reason it was less of a problem with the immersion heater was that the water was hotter, so you used less of it. The level didn't drop enough to cause a problem.

To prevent this happening you need the T to be below the lowest tank level possible, so raise the tank more, fit a shorter, fatter cylinder or move it back downstairs. Depending on the height of the T you may be able to re-plumb it nearer to the top of the cylinder, which could be the easiest solution.

HTH

Mark

Thanks for your response, but I'm not sure I agree with your explanation, probably because I've not explained enough about the system and therefore you don't have the full details.

Air gets sucked in immediately when I turn on the hot tap, it doesn't get sucked in when the water in the tank has dropped to a certain level. Before I changed to 28mm I could understand why a sudden gush of water to the hot tap could suck some water out of the vent pipe as well as the cylinder, but with 28mm feeding the cylinder (and that 28mm is copper) and 22mm plastic pipe (with inserts too) exiting the cylinder I couldn't see how, even with the difference in the head of height, the

I've also extended the vent pipe horizontally to compensate (slightly) for the much smaller head of water. I now have at least 6 feet of water in the 22mm vent pipe, albeit horizonally (slightly sloping upwards always) rather than purely vertically as normal.

This system HAS been working, when I changed to 28mm I tested and tested to make sure that the problem had gone away. The fact that it has come back either means that something is blocking the 28mm pipe from the tank to the cylinder, or that the change in heating device has effected it somehow. I can't think of anything else that could cause this.

I've noticed that since changing to heating via the coil the bottom brass connection to the cylinder (the one from the tank) now feels quite warm. I assume because the coil reaches much lower than any immersion element could. But could this cause a problem, could the difference in water temperature cause unwanted turbulence in the water when the cold water comes in to the bottom of the cylinder from the tank, and could this mean that I'm back to square one?

You'll notice that I d> > I posted this thread a few weeks ago

Is the cold header tank clean?

Just wondering if there is some crud getting sucked onto the outlet that is connected to the hot water cylinder - when you upgraded it, it may have shifted, but has now found it's way back to the outlet, and is partially blocking it?

Did you change the outlet when you upped to pipe size?

Sparks...

So how much below the lowest possible water level in the tank is the T? It's vertical separation that counts. How much below the full level too?

According to the textbooks the "top" of the T should be at 45 degrees, the "upright" at 45 degrees pointing downwards, such that any bubbles escape up the vent without entering the hot water feed. I think you've been told this before.

The original system in my house had a vertical "top" to the T and a horizontal hot water feed. Bubbles got into it and we used to get air in the hot water just like you. When I re-plumbed the house I did it as per the text books and haven't had any air in the water since.

By making the vent close to horizontal you've made a trap for all the bubbles generated by the heating coil. These are being drawn in and hence you get air mixed straight away. Maybe.

Plus there isn't enough vertical head, so after the bubbles are drawn in the effect of insufficient head comes into play, as Roger described in the previous thread. Again, maybe.

Post an accurate scale diagram somewhere for us and I'm sure someone will come up with the answer (though I suspect there are at least 2 issues, and that they have both been covered).

Mark

I'll post some pictures tonight, and label the appropriate parts (even experienced plumbers may not be able to determine what everything is in my setup ;-) )

Sparks wrote:

That might be the difference. Because the water is now cooler, it needs more hot to cold. If you are using a mixer tap, this might result in a greater hot water flow, if the limitation to the flow rate is the mixer spout.

Christian.

So....after what has seemed like years, the hot water flow is FINALLY fixed!!

THE CAUSE? a plastic cut-out disc from the cold water storage tank that I hadn't removed after drilling out one of the tank connector holes

HOW I DISCOVERED THIS? well I was installing a Surrey flange at the top of the hot water cylinder, and after removing the existing fitting I notice something bobbing up and down at the top of the cylinder - after fishing it out I discovered the cut-out from the recently installed cold water storage tank

AND HOW IS THE HOT WATER FLOW NOW? well the water is perfect! power shower works fine whilst all other taps are on in the house. this may have something to do with the new Surrey flange, but that damn plastic disc is (I'm convinced) the source of most of the problems!

HOW ANNOYED WAS I ? very ;-)

it was as simple as that!

cheers to all who showed an interest, Graham

snipped-for-privacy@yahoo.com wrote: