Communal attic tank permanently over flowing

[tonton]

The block of flats I live in has a large cold water attic tank with an overflow pipe that is permanently running. A plumber drained the tank and capped its supply, assuming no one in the block was still using it. Within two days (no idea how long though) the tank had filled back up and the pipe was running again. The cap is definitely working.

How could this be happening? I can see from outside that everyone in the block has flues for a combi (?) boiler, so could it be a faulty mixer tap or mixer shower in someone's bathroom is allowing mains pressure (hot, from the boiler) to backfill a pipe that is still connected to the attic tank?

 

[Madrab]

Usually with these types of communal setup there would be individual gate valve to each supply, presume they weren't shut down? It's also a bit strange that a plumber would have just fired in and capped and drained a communal attic cistern on the assumption that no- one was still using it, unless there was a notification made to all the occupants?

Just because everyone has combi's doesn't mean that someone's bathroom cold supply wasn't still connected though people would normally be pretty quick at shouting if their supply stopped all of a sudden.

If there is definitely no mains supply to the cistern then it can only be backfilling but as above, if someone's cold was still connected to it, you would expect them to be shouting about it.

 

[tonton]

I assume there are no gate valves, I'll have to check. That would certainly be an easy fix! People were notified, it's been a long-term problem we've not been able to resolve.

I guess it's possible for someone not to notice there was a lack of supply after draining the tank. The pump that drained the tank couldn't get the last few inches of water from the bottom and then the tank was backfilled shortly after. If it's a basin tap, maybe there would be no interruption in supply, or maybe they were away.

How likely is it for a mixer tap or shower to enable backfilling?

 

[Madrab]

How likely is it for a mixer tap or shower to enable backfilling?

Certainly could happen, the trouble would be to track it down. The other option would be to bung the cistern outlets or cut and cap the, the latter would probably be more permanent but the former just to test. How many outlets on the cistern is there?

 

[tonton]

Certainly could happen, the trouble would be to track it down. The other option would be to bung the cistern outlets or cut and cap the, the latter would probably be more permanent but the former just to test. How many outlets on the cistern is there?

At least four outlets. I did ask the plumber about capping them but he wasn't keen as they are lead. Bunging the outlets to test is a good idea though.

I wonder if there are valves on the outlets but he didn't want to turn them off, potentially subjecting them to mains pressure?

 

[Madrab]

I wonder if there are valves on the outlets but he didn't want to turn them off, potentially subjecting them to mains pressure?

Maybe, but would only be an issue if the valves were that frail that they would fall apart under mains pressure, hopefully they aren't that bad. If anything they would probably be gate valves and if they didn't shut down fully, which gate valve are notorious for doing anyway, then they would just pass into the cistern again. That being said if there were valves then they could be disconnected and capped at their connection compression point, if suitable imperial blanks/stop ends could be found.

It needs to be fixed one way or another, worst case would be the lead is cut and a lead loc or similar fitted. Ultimately though the offending source should really be found and fixed IMO. It can only be one of 4 locations, if that's the number of outlets.

Where is the cistern overflowing to, is it a warning pipe out from the eaves that just flows out and ends up on the ground? Is the property metered and everyone's paying for the wasetd water?

 

[tonton]

It's flowing to the garden from the eaves, but the pipe is not quite long enough so the water is damaging the wall, at ground floor mostly. We're not metered.

I meant the plumber was concerned about subjecting the lead pipe runs to mains pressure, not the valves.

 

[tonton]

I take it the mixer tap theory is a lot more likely than someone mistakenly connecting their cold supply from their attic to their mains supply?

 

[Madrab]

I take it the mixer tap theory is a lot more likely than someone mistakenly connecting their cold supply from their attic to their mains supply?

Yes, if they had cross connected a feed from the cistern to the mains, the cistern would overflow in minutes and it would be pretty obvious that it would be back filling.

I meant the plumber was concerned about subjecting the lead pipe runs to mains pressure, not the valves.

Ah ok, well shouldn't really be an issue, 10's of 1000's of lead pipes across the country carry mains water as we sit here.

Has it actually been established that the cistern is being backfed? It should be pretty obvious from just watching the outlets to see water entering the cistern. Sometimes, if it had been set properly, with a communal cisterns then the feed valves would have been tagged as to what property it served. If there are only 4 outlets though, then can it be established what properties they are connected to? If so then they can have the mains isolated to each one in turn and see when the flow stops.

 

[tonton]

I don't know if they're labelled, I'll see if I can find out. Yes, maybe you can see the water being disturbed due to the backfilling. I don't know how easy that is though now that the tank is full again, and also if the flow is very slow? Maybe you could put something like string or ribbon near the outlets and be able to see it moving.

It must be being backfilled as the pipe that was filling the tank originally has been capped before it reaches the tank; even if the cap were leaking it still wouldn't fill it. Thanks for your help.

 

[Madrab]

now that the tank is full again

It would need to be emptied again I guess. How was that done before, there would usually be a drain point. TBH I think this comes down to what the plumber was tasked with originally.

Ultimately they would be the ones to come up with these ideas and implement them to get to the bottom of why it's happening, he should have the experience, tools and procedures to get to the bottom of it.

 

[tonton]

It would need to be emptied again I guess. How was that done before, there would usually be a drain point. TBH I think this comes down to what the plumber was tasked with originally.

Ultimately they would be the ones to come up with these ideas and implement them to get to the bottom of why it's happening, he should have the experience, tools and procedures to get to the bottom of it.

He used a pump, presumably there is no drain off. Yes, I would like the plumber and building manager to handle it! After months of inaction, the building manager arranged the tank to be drained and capped (£500) and then declared it a 'private matter' when it continued to overflow. So we're trying to get the original plumber back or find a new one.

 

[Madrab]

He can't do that as far as I'm concerned. Just because it's been capped doesn't change the cisterns status from communal to private. The possible undercutting damage the overflowing water may cause as well isn't private it's communal, so I wouldn't accept that and take him to task over it.

 

[Nige F]

sounds like the B M needs his privates capped.

 

[tonton]

Yes, the damage it's causing and potentially will cause is definitely communal. And yes, the building manager is handling it badly!