Cold water tank emptying

[pmbpmb]

Hi all,

Hope you can help.

We've just had the mains feed up the drive replaced, and a water meter fitted. Usage seemed rather high to us.
So, we turned off the cold water feed to the tank in the loft and the meter stopped moving - we assumed it was leaky ballcock on that basis (it was dribbling). Happy about that, straightforward fix...

However, we just had a few days away and turned the water off entirely.
On switching it back on, it was quite clear that the tank was only half full (or so).
So we're assuming therefore that there's a leak elsewhere.

But...
Tank overflow is not dripping and tank itself is not leaking.
Only one cold tap (in the bathroom) is fed from the tank - and is off. Showers, toilets and cold taps elsewhere are mains fed (and aren't leaking anyway).
Central heating feed and expansion tank - nothing seems to be going on there.
That kind of says to me that there's a leak on the hot water system somewhere?
There's no wetness under the immersion or the boiler (or on the walls+ceilings).

Are we missing something? Is there anything else that could be causing the cold water tank to be continually filling (albeit at a dribble?) Is there anything else to try?

Hope you can advise. Not looking forward to the prospect of pulling up floors... Anyone any experience of a problem like this? How was it resolved?

Thanks in advance.

Cheers, all.

pmb

 

[terryplumb]

If you close off the supply to the cold water cistern after it is full of water, and don't use any hot water or any cold outlets that are fed from it ,how long does it take for the water level to drop ?
Are there any hot water pipes buried in concrete or in a void under ground floor?

 

[CBW]

What about a washing machine feed or an old connection?

 

[pmbpmb]

Hello terryplumb,

Thanks for the response.

We were away just under 2 days and the tank took a good 5-10 minutes to fill up once I opened the stopcock. I'm going to repeat the exercise tonight.

There's a hot and cold pipe running through concrete to a tiny sink in a downstairs toilet in the extension. (This was added to the house in the 1990s, before we bought it). When they ran the new supply line in they attached to the sink's cold water pipe.

All the other pipework is under wooden floorboards, I think.

Cheers,

pmb

 

[pmbpmb]

Hello CBW,

Thank you for the reply.

Washing machine and dishwasher are both mains fed, I think.

Washing machine can be isolated independently - but not dishwasher. Tried unhooking waste pipe from that into bucket a few weeks ago, but didn't see any leakage there.

Interested by your 'old connection' comment. What would I be looking for?

Cheers,

pmb

 

[terryplumb]

Do you have any toilets that are fed from the loft cistern , it's odd that only one cold tap is fed from it ?
Are the pipes under floor boards in a void ( crawl space in ground floor )?

 

[pmbpmb]

I will double-check but am pretty sure that the toilets are all mains fed. In any case they are all ok, I think - I refitted them last summer. Bog roll on the back of the pan is staying dry, and no overflows running.

 

[terryplumb]

Are the pipes under floor boards in a void ( crawl space in ground floor )?

 

[HERTS P&D]

Any push button toilets?

That's where the leak is normally found.

Andy

 

[CBW]

Interested by your 'old connection' comment. What would I be looking for?

Any previously used connection in the kitchen for a washing machine. I have seen it a few times, where they have been left in and a drip develops

 

[pmbpmb]

Hello terryplumb, Andy and CBW, and thank you so much for your responses!

I have double-checked all I can. Here goes...

- *All* the toilets are definitely mains fed (so with the mains water off I'm assuming they shouldn't affect the loft tank????)
- *Every* cold tap in the house, except for one bath tap, is mains fed. The one tank-fed tap is not (visibly) leaking.
- The outside garden tap is not dripping.
- Washing machine and dishwasher are tapped off from the same line that feeds the downstairs toilet, which is mains fed (so my layman's assumption is that they are mains fed also).
- Two electric showers are mains fed.
- Under the boiler is completely dry. I managed to get a section of floorboard up under it and there was nothing to see.
- Heating feed-and-expansion tank in loft is not calling for water (and is mains fed anyway).
- We have no visible signs of leaks: appliances are dry behind, and walls, ceilings, floors are all dry.
- Tank stand is dry, and no overflows are dripping. Cylinder cupboard is dry, no signs of wetness.

And yet the cold water tank is still emptying (albeit slowly). At the moment we've got the mains water off and I'll be checking the level later, but it does seem like something is going on. Obviously I'm not a plumber like you chaps, so I'm just trying to be logical, but my inference is that with the mains off and water still draining then there must be something specifically up with the plumbing supplying the hot water taps (rather than the central heating pipework).

I don't know whether this extra information helps:
- House was built in 1973 and extended in the 90s by the previous owner, adding an en-suite bathroom, downstairs toilet with sink and utility room. Ground floors in the extension are concrete, wooden in the original house.
- Most of the utility room cold water pipe is above the floor and runs to the toilet beyond. Washing machine and dishwasher come off this pipe. I think it then runs up the wall to the en-suite.
- I can't really tell where the downstairs toilet sink hot water pipe runs, but as it comes up from the floor must be completely under concrete except for any portion that might go under the kitchen floor. The en-suite is directly above, but I don't know how its hot water gets there.
- The cold water tank has the feed pipe in and two pipes out - one slightly fatter than the other and both fatter than the feed pipe. It replaced a metal tank about 5 years ago. Joints are dry.
- Boiler in the kitchen is a Baxi Solo 3 PFL 70, about 20 years old. It's had a handful of new circuit boards and fan units over the years.
- We had the new boiler put in when we moved here. It replaced an old gravity fed-system (so it's sat in a great big vented cupboard).
- Hot water and heating motorised valves in the cylinder cupboard were replaced last year (could no longer get the parts), along with the pump.
- Mains water feed in the drive was replaced in January this year. We thought we had a leak, water people said 'possibly a small one', so we had it done anyway. Turns out it was lead pipe in any case, so it was worth doing.
- Water meter was fitted a few weeks ago. Kept an eye on it and it never seemed to stop - we assumed this was just the cold water cistern filling up due to a dodgy ballcock, never getting to the overflow because of us using water. Isolating the tank all day (with the mains still running) stopped the meter moving - it never budged, so that seemed to prove the point. Anyhow, went away for a couple of days and - for interest - switched the water off at the mains. Was really surprised how long it took to refill the tank when the water was put back on.

So, it seems like the water's going somewhere - but I'm not sure what else I can try. At this rate we'll be going back to unmetered water, but that does seem a bit un-eco...

Any ideas? Thanks in advance once again!

pmb

 

[HERTS P&D]

I bet your toilet in your bathroom is tank fed and running down the back of the bowl.

Andy

 

[pmbpmb]

Hi Andy,
Afraid not. Just flushed it, it's not filling.
Cheers,
pmb

 

[opps]

Are you on a gravity fed heating system? If yes, might the water be running to the header tank?

BTW- I am not a plumber.

 

[CBW]

There’s should be a gate valve either on exiting the cold water storage cistern or in the cylinder cupboard where it feeds the cylinder. I would turn this off first and ascertain if the cistern still empties.