DIY Doctor

Bath Running out of cold water halfway through running the bath

Postby Richard1972 » Fri Oct 23, 2020 4:05 am

Hi all,

We have a low-pressure gravity system, with the water tank in the loft. We have always had a problem with cold water running out (i.e. if my wife has a bath and then I have a shower straight after (we have a power shower), more often than not the shower runs out of water halfway through - the cold water, not hot).

We had a massive water leak this week, which has resulted in a new water tank being fitted. It is smaller than the previous one, but still guaranteed to be a standard size for a 5-bedroom house (we have a 4-bedroom house).

Now, when we run a bath with both hot and cold running, it runs out of cold about halfway through filling the bath. The only way around it it seems is to run the hot water first, and then turn that off and run the cold water. The water is not being used for anything else (i.e. this is first thing in the morning, there is only two of us etc).

I don't think the fitting of the new tank is the fundamental issue (i don't think so anyway, but who knows) as we have always had this kind of problem. It seems to be that the tank is not filling up quickly enough.

Can anyone offer any advice how this could be resolved in any way ?

Many thanks,
Richard
Richard1972
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Postby stoneyboy » Fri Oct 23, 2020 7:38 pm

Hi richard1972
As you have diagnosed the CWT is not filling quickly enough and is not large enough to cope with you. Cheapest first solution is if you have good mains pressure - modify the pipe work local to the CWT so you have 2 ball valves. If this is not enough you will have to fit a second tank linked to the existing one but make sure there is a scouring action between the tanks.
Regards S
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Postby Richard1972 » Sun Oct 25, 2020 4:53 pm

Many thanks for the above.

I have measured the tank and it is 70cm x 47cm x 50cm. I think this means it is about 25 gallons ? So fundementally I think the tank is just too small, and probably needs a 42 or 50 gallon tank.

Also, I checked the water level. The tank is 47cm high, and the water (when the tank is filled and stops filling ) is only 21cm high. So less than half the height of the tank. Now I know the water wont come to the top of the tank, but this seems very low. What do you think ? So this morning, I pushed the ball valve down until it filled up another 10cm (upto 33cm), my missus ran a bath, and it filled the bath up fine.......just. By the time the bath was run, the water in the tank was just at the top of the screw things where the pipes come in. So right on the cusp. But it does mean that if the ballvalve can be altered, than this would be at least an option in resolving the issue.

i checked the water pressure coming in. It seems ok - when the bath is being run, and the tank is filling up, the water coming into the tank is like a tap being on. So think thats ok.

Just think it is a combination of the ballvalve maybe not being set correctly and agian, fundementally i think the tank is too small.

A new simlar tank (coffin) at 50 gallons is only about £150. I am tempted to just buy it, then get someone to fit it. Now that this tank has been fitted, which is also a coffin tank, i cant imagine a replacement tank being too difficult to fit.

Very interested to hear your views on the above.

Many thanks,
Richard
Richard1972
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Postby stoneyboy » Sun Oct 25, 2020 9:36 pm

Hi richard1972
Certainly your CWT is too small but you might get away with fitting a second ball valve. Cost probably 100-200 pounds.
Fitting a larger tank would be a better solution but would cost 450-650 pounds. This assumes the ceiling does not have to be strengthened.
Costs are approximate and depend on where you live.
Regards S
stoneyboy
Rank: Project Manager
Posts: 3853
Joined: Wed Dec 10, 2008 6:44 pm



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