Overflow Pipe constantly dripping

Smurts · 23-03-2026 02:00PM #1

Hi folks - just looking for a bit of advise - we recently got our attic renovated and they moved the attic storage tank (gravity system); it was moved further from the toilet/cylinder but at the same level. Since they moved it, the cold water pipe getting blocked and then causing an air lock; they flushed and cleaned the pipes a couple of times but this issue kept re-occurring. The hot water was ok, but the cold water kept getting blocked and then airlocked.

To prevent this happening again, the plumber connected the cold water feed upstairs to the mains supply. Ever since he did this, the overflow pipe keeps dripping - he changed the ballcock on the tank but it is still overflowing. He said its the water from the cylinder is back feeding up to the storage tank that is causing this - this is correct as when we turn off the valve on the cylinder the dripping stops. He is claiming that there is a hole in the cylinder coil that is causing this issue and that is it just a coincidence that it failed when he changed the cold water feed to the mains.

I am wondering if any of their works could have caused this issue as he is telling us it will be a significant cost to repair this, and it seems to me a very strange coincidence that this happened at the same time as the changeover to mains? Could the pressure have caused this issue, the plumber is claiming that the cylinder was always mains fed (we are not sure about this) so it couldnt have been anything he did and is just poor timing.

TheW1zard · 23-03-2026 02:05PM

Post a pic of the ballcock mounted to the tank. Does it stop dripping if you hold the bar up? Did he use a reinforcing plate on the outside of the tank?

Smurts · 23-03-2026 03:59PM

I will get a picture when I am home later, he said the old ballcock was broken which was what he/we thought was initially causing the issue so he replaced it but it is still dripping, which stops when we close the valve at the cylinder. I'll get a picture of the ballcock later, thanks for your response in the meantime!

TheW1zard · 23-03-2026 04:56PM

If there's any tension on it it will keep dripping. It needs to be horizontal with no tension. The plate is used to brace to ballcock to the tank, sometimes on both sides but definitely on the outside.

Thats my experience anyway and we got it sorted

Smurts · 23-03-2026 05:02PM

Noted, will check that this evening, thanks again!

Smurts · 24-03-2026 11:04AM

Yes there is a plate on the ballcock, and it seems to be working ok (it was only replaced last week). A little stream of water into the tank is noticeable in one of the bottom pipes into the tank so likely this that is causing the issue - the plumber was blaming the ballcock last week hence the confusion!

It is just concerning that we have been given different reasons for every issue hence the doubt that it is just a coincidence that the cylinder coil would leak at the exact same time as he switched the cold water feed to mains fed.

TheW1zard · 25-03-2026 12:16AM

The outlet for the overflow should be higher than where the ballcock comes to rest. From the pics the outlet looks to be too low.

ted1 · 25-03-2026 08:03AM

try bending the arm of the ballcock downwards so it’s sits lower

whizbang · 25-03-2026 11:33PM

cold water feed upstairs to the mains supply.

The only way mains water can be connected to the upstairs circuit is; it must completely disconnected from the cylinder, or completely disconnected from the tank.

there is no way they can be connected together without the mains water backfeeding into the tank. this is the source of the overflow.

I suspect 'plumber' put a Non Return Valve and a T to mains in outlet of tank. NRV are not intended for this purpose.

get the initial issue of the airlock sorted, and the mains connection isnt needed anymore.

whizbang · 25-03-2026 11:35PM

And get some insulation up there.. plumber is 100% liable when those pipes freeze ?

Smurts · 25-03-2026 11:50PM

Hi, re: the insulation - the place is fairly warm as the whole roof has been sprayed with insulation so dont anticipate that there'd be an issue with freezing.

The airlock was stemming from the pipes getting blocked (the pressure would drop over a few days and then stop completely and then airlock the system but it was the blockage that was causing it) The plumber flushed the lines a couple of times and couldnt understand why the pipe kept getting blocked - thats when he connected to the mains. A neighbour of ours who used the same attic company/plumber had the same issue and again he connected to the mains and solved their issue.

I spoke with another ex-plumber and he said that the issue is likely coming from the cylinder and a leak in the coil given that it stops when the valve is turned off (you can also see a small airflow in the water in the tank in the lower pipe feed from the cylinder).

I guess with all the issues to date since the tank was moved, we just thought it was an unbelieveable coincidence that there was no overflow issues at all until the exact time he changed to the mains! The ex-plumber who we were speaking to said it seemed very strange but the coils would be tested to 10 bar so anything they did on the conversion shouldnt have casued an issue.

Smurts · 25-03-2026 11:56PM

Apologies just re-reading your response - are you saying there will always be a backfeed even without a potential leak in the coil? If he changes back to the tank supply for the cold water we are concerned the blockage will happen again for the 4th time, as we are then left without cold water upstairs until the plumber comes back to unblock again.

You are correct in what he has done ie. there is a t junction feeding both the tank and the cylinder. He had mentioned about fitting a NRV but I am not sure if he did.

Overflow Pipe constantly dripping

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