Finding a hidden water leak

[JohnD]

Tie up the ball float in the F&E and see if the water level drops. Do the same in WC cisterns. IMO a leak that you can't see may well be under the floor, where there are usually lots of radiator pipes. If it is in a concrete floor, you may find damp if you roll back the floor covering. How old is the house?

If the leak is in or under a room, the humidity in that room will increase, if you leave the door and window tightly closed, for example overnight. On cold mornings you may see misted windows. Otherwise try some humidity meters.

You can put an inexpensive scent in the F&E rather than a dye.

 

[Lower]

Pinholed coil on the cylinder?
Chuck a teaspoon of drain dye into the CH header tank. See if your hot water changes colour. Might take a day or two.

no leaks from the overflows on the header tanks though so even if there was a pin hole if its not over flowing the header tank then you're not losing water.

 

[mcmoby69]

no leaks from the overflows on the header even if there was a pin hole if its not over flowing the header tank then you're not losing water.

But they will be using hot water, therefore keeping the level away from the overflow on the hot water header tank. I'm assuming that the heating header tank could be higher than the dhw header tank.
I had exactly same scenario last year, pressurised system with a leak. Spent hours looking all over the house, under floors etc.
I put drain dye in the towel rad and refilled the system. Couple of days later, hot water turned colour.
Customer had had a power shower fitted years ago, her loft tanks were replaced for a larger capacity. The water the ch was losing wasn't enough to reach the overflow on the dhw header tanks therefore it didn't drip.
In this scenario, it could be that hot water usage during the day is why these are not dripping.

 

[Lower]

But they will be using hot water, therefore keeping the level away from the overflow on the hot water header tank. I'm assuming that the heating header tank could be higher than the dhw header tank.
I had exactly same scenario last year, pressurised system with a leak. Spent hours looking all over the house, under floors etc.
I put drain dye in the towel rad and refilled the system. Couple of days later, hot water turned colour.
Customer had had a power shower fitted years ago, her loft tanks were replaced for a larger capacity. The water the ch was losing wasn't enough to reach the overflow on the dhw header tanks therefore it didn't drip.
In this scenario, it could be that hot water usage during the day is why these are not dripping.

The leak would gradually increase water level in the central heating header tank and there would be no mechanism for the header tank to drain, other than via the overflow, which the OP said isn't overflowing. I think your scenario is unlikely to be the cause of this leak.

 

[JohnD]

The leak would gradually increase water level in the central heating header tank

Provided that the F&E is lower than the CWC.

Do you know that to be the case?

 

[Lower]

Provided that the F&E is lower than the CWC.

Do you know that to be the case?

If it wasn't, there wouldn't be a leak anyway.

 

[JohnD]

If it wasn't, there wouldn't be a leak anyway.

Unless, for example, it was a joint in a radiator pipe out of sight beneath the floor.

 

[Lower]

Unless, for example, it was a joint in a radiator pipe out of sight beneath the floor.

In which case, the ball valve would be opening to replace the lost water.

 

[JohnD]

Tie up the ball float in the F&E and see if the water level drops....

 

[mcmoby69]

I think your scenario is unlikely to be the cause of this leak.

Let's not bother trying to rule that possibility out then. I suggest the OP gets a jcb in and rip all the floors up. Rather than drop a spoonful of dye in.........
Pinholed coils are unusual, only ever seen two in the 39 years I've been plumbing. 1st one hot water went manky, 2nd one just last year with drain dye. Customer had been quoted £1000 by a leak detection company, drain dye is £9 from screwfix. It's a no brainer.

 

[YorkshireMidge]

@mcmoby69 Certainly an interesting possibility and I agree, it shouldn't be ruled out. Our cold water tank and C/H header tank are sat alongside each other on the same timber platform in the loft - so a hole in the H/W cylinder coil would mean the greater/higher body of water in the cold water talk would force the level up in the small C/H header tank, and the latter would overflow. That seems a good way for things to happen as you wouldn't want C/H additives going the other way into your hot water.

But I can see if the C/H header happened to be higher than the cold water tank (which is the case in my parent's loft I think), at 0.5L/hr, it might not be enough even overnight to cause the cold water tank to overflow. However, the C/H header float valve would still have to be operating so simply watching it should be enough to prove it. The water in a C/H header is essentially stagnant and the float valve nozzle should normally be as dry as a bone - so the slightest trace of water from it would be a clue.

 

[mcmoby69]

Quote

But I can see if the C/H header happened to be higher than the cold water tank (which is the case in my parent's loft I think), at 0.5L/hr, it might not be enough even overnight to cause the cold water tank to overflow. However, the C/H header float valve would still have to be operating so simply watching it should be enough to prove it. The water in a C/H header is essentially stagnant and the float valve nozzle should normally be as dry as a bone - so the slightest trace of water from it would be a clue.

Unquote

Technically yes, but the two headers should be acting separately, the pinhole technically links the two together which is what I said before.
If the heating tank is above the cws the level will rise and overflow, unless the hot water being drawn off during the day keeps it below the overflow. How big is the cws tank? What is the gap between the water level and the overflow pipe? Will it rise to that level overnight when everyone is in bed. All these are unknown.
Vice versa, the level in the cws tank is irrelevant if it's lower than the CH header tank, even if the coil is pinholed. Water will always find its own level ( as long as they are linked)

The CH header tank, also know as an f&e system, would not be unusual to have an odd drip on the ball valve outlet. Due to system water evaporation and topping up etc. So, that's not a viable option really.

Drain dye in the ch header tank is the cheapest logical option to diagnose a difficult problem. If I'm wrong it cost the OP £10.
I may be 900 miles away from him/her, still cheaper than driving over.........

 

[MikeToll]

Sorry about the pause but thank you for the discussion ... which I can just about follow but I'm not experienced or knowledgeable enough (yet) to hold it all in my head long enough to arrive at an outcome!

1. I love the simple science of the drain dye / fragrance approach. So if I added drain dye to the F&E header tank I should hopefully never see it anywhere else (no pinhole leak in the coil) but if I do see it again from hot taps then we're in to the realm of draining down for a new tank/coil and afterwards back to new fresh clean hot water with no dye in.
Have I understood that correctly?

2. Re. testing the dryness of the CH F&E inlet valve; the CH F&E header is a smaller tank than the DHW header and both are sat on the same platform.
Does that help arrive at the validity of testing the dryness of the valve as an indicator of a pinhole in the coil?
If not then what's the key info needed and I'll go find out.

Thank you all so much for sharing your knowledge, these forums are a great resource for learning.

 

[JohnD]

Tie up the ball float in the F&E and see if the water level drops. Do the same in WC cisterns.

 

[YorkshireMidge]

@MikeToll If your cold water tank and C/H header (aka F&E) are at the same level, and the latter is smaller which is what you're telling us (see left hand side of diag below), a pin hole in the coil would result in the water level in the C/H header being raised to the point it overflows. I'm pretty sure you'd have noticed the water level being right up to the overflow pipe in the C/H header AND/OR water dripping out the overflow outside for that tank. So, it seems doubtful you have the pin hole issue, and there is little point in adding dye to the C/H header in your case anyway.

Had your C/H header been ABOVE the level of the cold water tank (right hand side of my diag) dye in the C/H header would be useful in proving a pin-hole because the dye would work its way into your hot water circuit.

To keep things simple, there are only three circuits the water can be leaking out in your particular case, so it would be a good and positive step to at least work out which of the three it is.

1. Mains cold
2. Hot (and low pressure cold for bath taps)
3. Central heating pipe work (rads, interconnecting pipes etc.)

So I would do the following in your position:

Tie up BOTH float valves in your cold water tank and C/H header so they can't operate. If your meter is still going around, you have proven within a couple of minutes that the fault is in mains cold. If your meter stops going around, release the cold water tank ball valve, and put a marker in the C/H header tank at the current water level - and just leave it for a few hours and see if the water level has dropped. If it has, the fault is your central heating somewhere. If it hasn't, it must be in your hot water (and low pressure cold for baths) circuit.


Finally, a random thought on hidden leaks which I don't think has been suggested yet. We have a twin impeller power shower pump (tank fed from hot and cold tanks) and that goes to a flush fitting thermostatic mixer within our en-suite bathroom wall. If either of the input unions were leaking, I would know about it as the valve is fully accessible from behind in our case. But I have come across some cases where they are not - and that might give rise to a hidden leak within a wall.

Also, if you have a bath, are the taps against an outside wall? If so, a leak from a bath tap union might see water running down the pipe and into the wall cavity rather than dripping onto the ceiling below.