Cold water tank overflowing (Not ball valve) All aspects of plumbing questions and answers, help, tips and information

[Nik C]

Hi,
i would appreciate advice or suggestions.
I have recently had some building work done in the house, including some plumbing work. Had a few new mixer taps installed downstairs including a Quooker tap. Plumber had trouble establishing cold water pressure and i note most seem to run off mains.
Since this time i have noticed the cold water tank is overfilling.
We have a gravity fed system and a pump that covers upstairs shower, bath and sink. Had a new ball valve installed in cold water tank, still overfilling.
No noticeable water coming through vent pipe. One of the 2 cold water pipes running from the cold water tank is sometimes warm, although i have not been able to discern the pattern of this occurrence. Not sure exactly when the tank is filling up but most obvious during the evening. Even if no water has been used and hot water cylinder is not heating up the level will rise in the cold water tank, from say 8pm - 7am.
Any suggestions or things i can try to identify the problem?

[stoneyboy]

Hi nik c,
You need to look at any device that has both hot and mains cold feeding it. If a device has not been used for a while the mains cold feed will be getting close to room temperature, so if you find one that is mains cold temperature this may be the culprit with mains cold feeding into the hot system and back filling the cold water tank.
Regards S

[Nik C]

Stoneyboy,
Thanx.
I have tried testing the mixer taps we have but cannot discern a significant difference in Temp. (This may be my abilities as i am not a plumber or at all 'Handy' round the house!)
I have noted that the pipe that is getting warm in the loft which goes from the cold water tank, appears to get warm when the immersion is on?
Anyway thanx agian.

[stoneyboy]

Hi nik c,
Ok try another way, you should have isolating valves on the pipes supplying your taps. Try turning the mains feed off to each tap in turn and see if the cold water tank stops filling. You may have to do this overnight to isolate the problem.
Regards S

[Nik C]

Stoneyboy,
thanx. Appreciate your advice.
Will investigate this!

[stoneyboy]

Hi nik c,
The other question I would ask is whether you have a header tank for your CH and is this higher than the cold water tank. If you to both these the coil in you hot water tank may have perforated.
Regards S

[Nik C]

Hi, stoneyboy just wanted to say thanx for all your advice. I got a plumber round and he was able to isolate which tap was at fault and shut off the hot water so after a day or two i could see the cold water tank had stopped over filling. He says he will put a non return valve and that should resolve the issue.
Thanx again
Nik

[scody]

One of the things that happens a lot is failing to put a non-return valve on the hot water line to a mixer tap; in a gravity system this can cause all sorts of problems, as you've discovered. If anyone reading this has a mixer tap, have a look underneath at the hot water feed. If it doesn't have a one-way flow valve on it (see image example) then I recommend fitting one; it's quite easy.

This type of valve stops the the mains pressure pushing the hot water back up the pipe to the tank, at the very least cooling down the water you've just paid to heat up (so you end up paying twice in effect). This is happening if you run hot water out of the mixer and then, a minute or so later, have to run it for seemingly ages to get it to become hot again. That is a giveaway symptom that the person who put your plumbing in was cutting corners. :-)