Hot water cylinder too small?

[neil7744]

Hi,

Right I've got a question that I thought was obvious but after doing a search on here and a bit of reading I'm now not too sure.

I have a gravity fed system with a 96 ltr indirect hot water tank.

When we moved into our house I fitted a bath and pumped shower.

Whenever we fill a bath the hot water runs cold after the bath is just over 50% full. Likewise having a shower if you stand in there for too long then it runs cold.

My thought straight away is the hot water tank needs replacing for a bigger one? I've had a little play with thermostats etc to compensate but either way it's not up to the job!

Any thoughts?

In a previous post someone said it wasn't the hot water storage tank but the feed?

 

[Kev F]

It's not the size as that cylinder should fill a bath, I'd leave the hw timed on once ie 6am to 11pm, try that or just put it on constant for a test. I'd say the cylinders full of crap, also check where your cylinder stat is, should be about 6-10 inches from bottom of cylinder, any higher and your only heating half of it

 

[gas112]

How big is your bath and how long do you spend in the shower ?

 

[neil7744]

Right the hot water cylinder thermostat is 14" up from the bottom of the cylinder (that's to the centre of it).

I think my bath is around 170 lts. I might have to double check that though!

The water stays at a constant temperature when I shower for about 10-15 minutes, but depends on where I set the valves. Because the shower is pumped there is one hell of a flowrate!

 

[neil7744]

As for the central heating system I've left the water on 'constant' and tried what you have suggested with the same results!

I can get the shower to last longer by turning up the hot water cylinder thermostat to a higher temperature so I only have to 'crack open' then hot water valve on the shower but this isn't great as both myself and partner have nearly scalded ourselves. This kind of works when filling the bath aswell.

 

[Kev F]

Stats too high

 

[Agile]

You are clearly expecting 200 litres from a 100 litre cyinder!

There is a simple solution and that is to get a water meter and then you will not over fill your bath or over stay in the shower.

Baths and showers are intended as a washing task and not a time using pastime!

Tony

 

[neil7744]

Ok,

Can you help me a little more as im not sure what moving my stat will do?

Am i right in thinking if my hot water is selected to 'constant' and everythings heated up as expected, if i tried to fill the bath purely on hot water i would only get 96 lts (ish) of hot water as thats all my tank holds before it would run cold? I havent tried this yet as usually i set the temperature on the mixer and leave it to fill, but when i return its uaully cold!

 

[Agile]

Moving the stat down will give you a few percent more stored hot water.

But its not going to be a mind blowing change and probably one you would not even notice!

Tony

 

[neil7744]

Tony,

when you move into a place first of all with no shower, to another place with a 6kw electric shower which kepps cutting out, to another electric shower that has an appauling flowrate in winter, its nice when you buy a house to have some luxury!

 

[Charnwood]

Is the setting on the 'stat too low, perhaps?

 

[Dan Robinson]

If the stat is half way up the cylinder, it will heat half the cylinder.

Lowering the cylinder stat will mean more hot water.

An average bath filled to overflow (when you get in it anyway) will be around 126 litres.

Not all of that will be hot water as you will mix in cold too.

 

[JohnD]

is the cylinder heated by an immersion heater or a boiler?

is the cylinder insulated or can you feel how low it is hot?

what temperature is the hot water?

if a boiler, is it switched on when you start to run your bath? is the boiler to cylinder flow pumped?

edit
you say it is gravity feed. If you change it to pumped, and if you have a modern cylinder, it will heat in about 20 mins. So if you take 10 mins to run the bath, in that time there could be an extra half-cylinder of water heated up.

 

[neil7744]

the tank is heated by a boiler.

the cylinder is insulated.

the cylinder is hot.

the thermostat on the cylinder is set to approx 60 degC. I have adjusted it and this does alter the water temperature quite a lot.

when the shower or bath is running yes the boiler switches on no problem. The boiler circuit is pumped. Pump is set to '1'.

I know you guys talk about the height of the cylinder thermostat, but what about the side of the hot water cylinder? Currently the thermostat is close to the boiler feed and return pipes to the coil, could this make a difference?

 

[Dan Robinson]

It will make a slight difference - but the height is much more vital.


This is of course assuming your cylinder is not caked in scale and sludge internally.