Bath running out of cold water halfway through running.

[Richard1972]

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 guarenteed 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 just 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 fundemental 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

 

[SimonG]

Cold water tank undersized or low mains pressure that cant replenish tank quick enough or problem with tank inlet valve.

 

[Ben-gee]

Should be 50 gallon minimum.
Was a new ball valve fitted with the new tank - should have been but you never know.
If the ball valve is new and it’s still slow to fill due to low mains pressure , try swapping the white plastic valve seat for a red one.

 

[snowhead]

Does the water bounce off the bottom of the sink in the kitchen when you turn on the cold tap?

Is there a Stop tap in an airing cupboard below the tank or elsewhere that's part turned off, assuming there is one in the loft that's been used to isolate for the new tank?

Are there any new style Isolation valves used on the feed to the tank?

Is it copper or plastic pipe that feeds the mains cold to the tank?

 

[Richard1972]

Should be 50 gallon minimum.
Was a new ball valve fitted with the new tank - should have been but you never know.
If the ball valve is new and it’s still slow to fill due to low mains pressure , try swapping the white plastic valve seat for a red one.

Thanks very much. I have gone up there today and measured - its 70cm x 50cm x 50cm. Which by my calculations means its a 38 gallon tank. Which is probably the answer.

 

[SJB060685]

It sounds like one of the above. I will also add it sounds like the feed to cylinder is tapped in lower in the header tank than the cold feed to house. This is not desired and should be the other way round to prevent momentary scalding in a case such as this.

 

[Ben-gee]

Thanks very much. I have gone up there today and measured - its 70cm x 50cm x 50cm. Which by my calculations means its a 38 gallon tank. Which is probably the answer.

You might think that, but it is actually only a 25 gallon tank; only approx 2/3 of the tank volume is “useable”.

And yes if you have a pump it is definitely not big enough.

 

[Richard1972]

You might think that, but it is actually only a 25 gallon tank; only approx 2/3 of the tank volume is “useable”.

And yes if you have a pump it is definitely not big enough.

Thanks for that. Ok - so i have gone up today and checked the water level. The water tank itself is 47cm high. But the water only comes up to 23cm. How high would you expect it to come up ? Using 2/3, I would make that 31cm. I pushed the ballcock down, filled it to 33cm and ran the bath. It filled up just fine......just. Any less and I think we would get problems. But if it filled to about 33 I think we would be ok and not need a new tank. Presumably the ball-cock can just be altered somehow to allow more water to fill up ?