Tank in attic overfilling from cylinder

fandango1

Our overflow pipe started flowing continuously. Initially thought it was a faulty ballcock, so replace that but the water kept flowing.

After much headscratching and various tests I discovered that the tank was filling via a pipe at the bottom of the tank that is connected to the bottom of the hot water cylinder. I presume this pipe is there is keep the hot water cylinder topped up as water is drawn off.

Can anyone advise how/why water is being forced back up this pipe to the attic storage tank and what can be done to fix it?

Set up is as per the attached file and the dotted line is the pipe in question.

Thanks very much.

Billy Bunting

Is the expansion tank higher than the main tank ?

yoshytoshy

It doesnt happen often ,but sometimes the coil on the cylinder leaks.
if your mains fed heating was passing ,it could fill the tank.

Im on a small smartphone ,but your photo looks like the mains is going directly into the flow.

Billy Bunting

The photo is a drawing, and its %%a%, does sound like coil but his drawing doesnt help.

Buford T Justice

Is the OSV pipe blocked?

fandango1

@ Billy Bunting: thanks for the generous praise for my artwork I claim to be neither plumber nor artist!

@ Fingers: I don't know what an OSV pipe is.

The leaky coil seems plausible as the central heating pressure has dropped dramatically too. Is a new cylinder the only solution?

yoshytoshy

fandango1 wrote: »

The leaky coil seems plausible as the central heating pressure has dropped dramatically too. Is a new cylinder the only solution?

It's easy to find out if the coil is leaking ,just isolate the feed pipe on the heating system. Either blank it off completely for a while or disconnect it. Draining the heating is the fastest way to know if it's the coil.

The pipe fingers is talking about is the open vent pipe ,never heard of one getting blocked but they can airlock if they're not done right. That would be pretty dangerous aswell ,but I've never seen that happen in nearly twenthy years (thank god).

Buford T Justice

If the heating coil in the tank was leaking wouldn't the water from the heating foul up the dhw and you'd have brown water coming out?