Help! Overflow dripping - ballcock/valve not the problem

[jevon99]

Hi - as I'm sure will quickly become apparent, aside from the basics, I know very little about plumbing! Therefore I am appealing to you beautiful, full of wisdom, people (flatter flatter) to help with a strange (or maybe not) problem.

The overflow from the cold tank in my loft has been dripping for some time. Not constant, but a few hours every day. On inspection it looked like the original ballcock/valve is still in place (50 years old), but, rather than replace, I thought I'd change the washer. - stripped out, changed washer, replaced. No problem.

However, it made no difference to the dripping - rats...
Finally I went the whole hog and replaced the ballcock/valve last weekend. Simpler job than I thought it would be and I was quite chuffed with myself. However (and here's the rub) THE OVERFLOW IS STILL BLEEDIN' DRIPPING!

The new ballcock/valve is functioning perfectly - not dripping at all on shut off, and the level that it shuts off appears to be a good few inches below the actual level of water in my tank - so the only thing I can think of is that water is entering the tank somewhere other than through the ballcock/valve. This is where I show my ignorance...

Is this possible? Where is it coming from? & How do I sort it out?

Any help gratefully received and appreciated

 

[Softus]

Assuming that this is the cold storage cistern (i.e. not the heating F&E cistern), then it's likely that you have unbalanced supplies to a shower valve.

If none of these, then other mixer valves can be culprits.

To test this theory, shut off the cold mains supply to the house while the dripping is in progress, and it should stop.

If it's the F&E, then it's likely you have a split or holed coil in a DHW copper cylinder.

 

[clf-gas]

Could be hot water venting, did citern feel warm ?.

Assuming that this is the cold storage cistern (i.e. not the heating F&E cistern), then it's likely that you have unbalanced supplies to a shower valve.

If none of these, then other mixer valves can be culprits.

I concurr, have had this today with mixer deck on a bath.

 

[jevon99]

Yep, it's the cold storage cistern, not the F&E tank. If I understand you right, water's getting into it through that pipe in the corner pointing down into the tank from a mixer valve? This must be the shower unit in bathroom, as I don't think there's anywhere else in the house the feeds are mixed....
Would the shower unit itself need replacing, or is it fixable?

Sorry to be so clueless...

 

[clf-gas]

The pipe bent over in the corner is the hot water vent pipe.

Turn on your shower and see if the overflow is running then check if water is coming from the vent.

 

[Softus]

Yep, it's the cold storage cistern, not the F&E tank. If I understand you right, water's getting into it through that pipe in the corner pointing down into the tank from a mixer valve?

We're probably using different terminology, so to clarify...

The pipe from the cistern to the hot water tank is the 'cold feed'. In the situation I suspect you're suffering from, water is being forced back up the cold feed and causing the cistern to fill and eventually overflow.

The pressure causing this backflow is coming from a shower mixer valve which is supplied with hot water from the hot tank and cold water from the cold mains. The pressure difference between these two can cause a fault in the shower valve that lets water from the cold supply cross to the hot supply.

This must be the shower unit in bathroom, as I don't think there's anywhere else in the house the feeds are mixed....
Would the shower unit itself need replacing, or is it fixable?

Some people say that a non-return valve in the hot supply will fix it, but I've never had any success doing that.

A quick fix is to insert a pressure limiting valve in the cold supply to the shower, and turn down the pressure to match the hot. You can determine an approximation of your hot supply pressure by measuring the vertical distance from bottom of cold cistern to the shower head, and dividing by 10, e.g. 1 metre == 0.1 bar.

A more expensive, but better, remedy is to install a pressure equalising valve before the shower valve.

 

[Softus]

The pipe bent over in the corner is the hot water vent pipe.

Turn on your shower and see if the overflow is running then check if water is coming from the vent.

Eh? Why do you think water will come from the vent?

 

[bobthebender]

Is your cold water tank higher or lower than your feed & exp tank ?

 

[clf-gas]

Path of least resistance, vented from hot water draw off.

Thinking of a job several years ago when this was the case

 

[jevon99]

Is your cold water tank higher or lower than your feed & exp tank ?

They're the same - that is to say, the bottom of the tanks are level with each other, although the cw tank is obviously much larger and taller....

 

[Softus]

So, jevon99, do you need any more information?

 

[bobthebender]

If the tanks are level and it is the overflow from your cold feed tank that is running then it counts out the cylinder coil as this would run from the f/e tank in this case.
Look at what the others say...Mixer/shower tap

 

[Softus]

Princess Diana is dead!

 

[bobthebender]

Princess Diana is dead!

You never ruled out the coil.
I just did
And your comment....."Eh? Why do you think water will come from the vent?"
Made me laugh did that
Was it a 5 week course you did
I won't tell anyone

 

[Softus]

What I chose to do was outline what I expect to be the likely cause, and ask the OP to test the theory. Time will tell whether or not that hunch was correct.

You never ruled out the coil.

I didn't claim to have done, but I was the first one to mention it on this topic.

I just did

And your comment....."Eh? Why do you think water will come from the vent?"
Made me laugh did that

In which case you'll be able to say why you think water is coming from the vent.