Running a bath drains the tank

[pmx_super]

Hi,

Before I can run a full bath my cold feeder tank runs completely dry. I'm guessing that this is symptomatic of a small tank (it's 25 gallons), a big bath (it's a corner bath) and poor flow rate from the mains feeding the tank.

Even though I understand the problem I have no idea what the most practical solution is. Can I improve the mains feed into my tank somehow (I'm in a 2nd floor flat)? Whilst space for a bigger tank is pretty limited, there is some room to play with - does anybody make 'made-to-measure' tanks?

Thanks
James

 

[JohnD]

a couple of tests:

see how many litres per minute you get at the kitchen tap (I assume this is mains-fed) by filling a bucket.

see how many litres per minute the bath tap supplies

see how many litres per minute the ball-cock in the cold water tank delivers.

this will give an idea of what the flow currently is.

If you have a convenient stop-cock that allows you to turn off the supply to the cold water tank, turn it off, remove the working part of the ball-cock by undoing the large plastic ring, and see what the flow rate is from the open pipe. If this is a lot better, it is possible to fit a larger ballcock that allows water to flow faster with less obstruction.

Have you got one of those round copper cold-water tanks fixed above your hot cylinder? Or have you got some kind of loft where a tank could go? (they are very heavy when full) What are the dimensions of the space available?

 

[pmx_super]

a couple of tests:

see how many litres per minute you get at the kitchen tap (I assume this is mains-fed) by filling a bucket.

see how many litres per minute the bath tap supplies

see how many litres per minute the ball-cock in the cold water tank delivers.

this will give an idea of what the flow currently is.

If you have a convenient stop-cock that allows you to turn off the supply to the cold water tank, turn it off, remove the working part of the ball-cock by undoing the large plastic ring, and see what the flow rate is from the open pipe. If this is a lot better, it is possible to fit a larger ballcock that allows water to flow faster with less obstruction.

I can do the first 2 tests, but testing the flow into the cold tank would be rather tricky. Access is horrendous (a wardrobe has been built around the walled-in airing cupboard).

Have you got one of those round copper cold-water tanks fixed above your hot cylinder? Or have you got some kind of loft where a tank could go? (they are very heavy when full) What are the dimensions of the space available?

I have a black plastic rectangular tank situated directly above the cylinder in the cupboard. There's another flat above me, so no loft space. The space available is 660x840 (WxD), with loads of vertical space (I'd guess there's 1m between the top of the cylinder and the ceiling).

I was looking around on the internet and found these combination cold tanks & hot cylinder units which look like they'd do the job nicely, though one's in Scotland and the other in Ireland..

http://www.lycrisbyrne.com/combo2.html
http://www.mcdonald-engineers.com/products/timesaver.htm

 

[giblets]

It's possible that the very small nozzle in the ballvalve serving the cold water tank has become blocked with scale so the water is only dribbiling into the tank. You will need to turn off the mains water and dismantle the ballvalve to clear it out.

 

[JohnD]

...or ft a new one, which is easier and quicker, especially in a difficult spot. You can usually leave the "stem" in place and just change the working parts (undo the large ringnut)

 

[pmx_super]

I've had a new stop valve fitted quite recently. I've actually had it changed twice in the last 3 years. The last two were leaking, causing water to continuously drip from the overflow pipe.

 

[JohnD]

was the flow equally poor with all the valves?

 

[mikej2005]

Would getting mains cold direct to the bath tap help ?

Even if the mains pressur/flow is low, at least it won't run out !

 

[pmx_super]

was the flow equally poor with all the valves?

The original one was fine until it started leaking, then when it was replaced the tank started running dry. I complained to the plumber and he fitted a low pressure valve which sorted things out.

It was replaced again more recently. I reminded him that he should use a low pressure valve because of the problems last time, but the tank has started running dry again. He has assured me that he fitted the same type of low pressure valve.

 

[Softus]

Well, you could DIY? Or not?

 

[JohnD]

so the problem appears to be connected with restricted flow through the ballcock.

If the tank is fed from the mains (and not from another tank) then a high-pressure valve is correct.

you could also fit two valves fed from the same pipe. Although this will not actually give you twice the flow, it will be more than one.

It might also help to take off the valve and let the pipe gush for a minute, this might wash out sediment, drowned earwigs, freshwater shrimps etc

 

[pmx_super]

It might also help to take off the valve and let the pipe gush for a minute, this might wash out sediment, drowned earwigs, freshwater shrimps etc

Sounds like I might find something nice for dinner too

 

[pmx_super]

would a 22mm ball valve (as opposed to a 15mm one) improve things do you think?

 

[JohnD]

if you mean float valve (aka ball cock) they come in half-inch and three-quarter inch, and yes, you do get more flow through a 3/4" as it has a bigger aperture.

 

[pmx_super]

Yeah, that's what I meant.

I often see 1/2" / 15mm and 3/4" / 22mm on specs for plumbing parts, as if they were the same thing. What's that all about???