Understanding hot water systems

lstar337

In our flat we have a hot water cylinder with immersion heater, and no cold header tank. I believe (but could be wrong) that this means we have an unvented hot water system.

The thing I don't understand, is that all the places I have visited on line are calling it a high pressure, high flow hot water system. But our system has a pathetic flow rate and no pressure at all.

I understand the basic principles of an unvented system, the hot flowing out should be roughly the same pressure/flow as the cold coming in. This isn't the case in our system, the pressure and flow of the cold is very high. It is so high that it splashes out of all the sinks, and damn near takes a layer of skin off if you have the shower set up wrong!

The hot on the other hand, well that virtually dribbles out of the kitchen tap, and the bathroom tap is only slightly better. I can stop both taps easily with my thumb, which is far from true with the cold.

I don't understand where the flow/pressure is going. I am no plumbing expert, I only know what I do from searching out this problem on line. Have I oversimplified the unvented system, is there something I am missing?

Thoughts appreciated.

thefishdude

if you have a hot water cykinder then the hot water is comming from that. does it have a stop !!!! or anything that can be turned to turn off the flow from the tank? maybe it is not fully open and so restricting the flow ?

keystone

lstar337 wrote: »

In our flat we have a hot water cylinder with immersion heater, and no cold header tank. I believe (but could be wrong) that this means we have an unvented hot water system.

The thing I don't understand, is that all the places I have visited on line are calling it a high pressure, high flow hot water system. But our system has a pathetic flow rate and no pressure at all.

I understand the basic principles of an unvented system, the hot flowing out should be roughly the same pressure/flow as the cold coming in. This isn't the case in our system, the pressure and flow of the cold is very high. It is so high that it splashes out of all the sinks, and damn near takes a layer of skin off if you have the shower set up wrong!

The hot on the other hand, well that virtually dribbles out of the kitchen tap, and the bathroom tap is only slightly better. I can stop both taps easily with my thumb, which is far from true with the cold.

I don't understand where the flow/pressure is going. I am no plumbing expert, I only know what I do from searching out this problem on line. Have I oversimplified the unvented system, is there something I am missing?

Thoughts appreciated.

Let us understand first what you have actually got there. What is the make/model number of your cylinder and if possible, can you uplift a pic of it and the pipework around it please?

Cheers

lstar337

This is the tank:

lstar337

Its a poor picture, but I am at work at the moment. The pipe on the bottom right is the cold in, that has a screw tap on it, but it is fully open. The pipe on the right about mid way is the hot out. This has a red tap on it which seems to be fully open too. That appears to be all the pipe work there is.

lstar337

Here is the label, though it is pretty useless: http://img17.imageshack.us/img17/8497/nhdy.jpg

keystone

Its not an unvented so you won't have hot water at mains pressure. Nor is it a thermal store which would also give you hot at mains pressure.

Its a vented combination cylinder where the top part is of the cylinder is your cold water storage and the larger bottom part is the hot water storage.

Diagramatically it might look like this:

or like this:

you'll have to get your head up into the top of the cupboard to find out.

The hot water pressure is totally dependent on the head between the cold water store and the hot water cylinder. In your case the head is virtually zero so the pressure and the flow is poor. This is accentuated becuase (most likely anyway) the cold taps are fed direct from mains.

Your solution is to pump the output from the cylinder.

Get someone in to look at it for you and quote.

Cheers

lstar337

Thank you Keystone for your excellent explanation.

We are on a single level, so the height difference between the hot taps and the output on the tank is about 500mm at the most.

Is there any minimum acceptable flow/pressure for the hot water?
We are renting and the landlord is rarely interested in doing any work which is (more or less) only for our convenience.

The main issue we are having at the moment is that the flat has a hot fill washing machine, and it never draws from the hot because the pressure is too low to activate the valve. This means all our washes are cold washes, because the machine cannot heat its own water.

keystone

lstar337 wrote: »

Thank you Keystone for your excellent explanation.

We are on a single level, so the height difference between the hot taps and the output on the tank is about 500mm at the most.

It will be poor unless you giuve it some help.

Is there any minimum acceptable flow/pressure for the hot water?

Purely subjective I'm afraid. Theres nothing in regs if thats what you mean.

We are renting and the landlord is rarely interested in doing any work which is (more or less) only for our convenience.

Inevitably

The main issue we are having at the moment is that the flat has a hot fill washing machine, and it never draws from the hot because the pressure is too low to activate the valve. This means all our washes are cold washes, because the machine cannot heat its own water.

Your washing machine or his? Bear in mind that even if it were able to draw hot water it has to empty several feet of cold water out of the hot pipe before any hot ever comes. If its your machine then it looks like time for replacement anyway because it must be horribly uneconomic to run.


Cheers

lstar337

Do the combination tanks always have a noticable sepparation, like this ->


Our tank doesn't seem to have that (though it could be hidden internally).

keystone

No they don't but then again thats a Fortic (which you don't have) and not a Gledhill (which you do). A clue is on the label where the "combination" box has been ticked coupled with the lack of any pipework which would indicate otherwise.

Cheers