Baffled by this.hot into cold tank.

[Timmyturtle]

I have a problem with someone's cottage.
Gravity hot water and upstairs cold.
Oil boiler,room stat,cyl stat 2x 2 port with auto bypass.
The customer noticed the overflow dripping,so I went into the loft and looked into the tank.
Ball valve shut but water flowing up the hot water vent.
The expansion tank is lower than the cold tank.
I had no control of hot water 2 way as someone had obliterated the front of the cyl stat so I couldn't even see what it was set at.
I replaced the cyl stat and noticed the zone valve was not shutting fully,so I replaced the zone valve( I could blow through easily when shut)
Boiler is 18 months old set quite low,pipes are normal heat at airing cupboard
The downstairs cloakroom has a hot gravity/mains cold single lever tap,I can't hear any transfer noises from here.
The pipe work from cylinder ,comes out the cylinder to the back of the airing cupboard then up into the loft. It must then split to feed the house and then vent. It is old 3/4 pipework been working for years ,though I can't see about 2metres of it as the rear loft has no access .
Any ideas why hot is running into the cold tank?
Thanks.

 

[Agile]

You need to test to eliminate a mains leak into HW.

Then to prove that the heating coil in the cylinder is leaking!

Tony

 

[Timmyturtle]

It runs into the tank even when ch pump is not circulating.Expansion tank is lower than main cold tank and no signs of expansion tank ballvale operating.
Unfortunately the mains stopcock does not fully close the water supply off and has been fitted behind a kitchen unit where it's very difficult to get at.
I will tell her it needs to be done and go from there. Thanks

 

[Agile]

You dont seem to understand how a cylinder with leaking coil behaves!

You may need a colleague who understands heating systems.

 

[Timmyturtle]

If the expansion tank is lower than the main tank it cannot leak into the main tank as it has less gravity pressure,it would fill the expansion tank up,not the other way round.
Thanks

 

[Agile]

You did not write the OP clearly.

Which loft tank is over flowing?

Or is it leaking out of the vent pipe?

 

[Timmyturtle]

I have a problem with someone's cottage.
Gravity hot water and upstairs cold.
The customer noticed the overflow dripping,so I went into the loft and looked into the tank.
Ball valve shut but water flowing up the hot water vent.
Any ideas why hot is running into the cold tank?
Thanks.

Its the cold tank,overflowing because the vent is filling it
Thanks again

 

[Agile]

Are you 100% sure its not the CH vent pipe?

I dont imagine any normal situation for a correctly installed system to be able to do that ( without a pump! ) as it defies gravity!

 

[Timmyturtle]

I can't see where the pipes enter the loft so I'm unable to trace it back. They built the pipes into an inaccessible area for some reason. The expansion tank also has one going over the top,but I guess it could be they are the wrong way round.
I did plug the exp vent when changing the zone valve and seemed to drain-easy ok, but as the zone valve is quite high in the system,not much would be expected from there anyway.
My only other thought was mains mixing at that tap.
All the other taps have their own hot and cold separate handles.

 

[HERTS P&D]

Out of interest, what trade are you Timmy?.........Handyman?

Andy

 

[Agile]

If they were crossed and the EX tank vent was lower than water level in the cold tank then water would run from that.

Even if a tap WAS leaking mains into the hot supply that would just run back into the tank and not out of the vent ( unless there is a blockage! ).

Something is wrong!

 

[stardanny]

Turn off cold supply to cloakroom's basin tap and see if it stopped, if it has, it is knacker.

If it is the hot vent pipe, the one over cold tank ( the large one ), I don't see how that vent pipe running over, it should back up via cold feed to cylinder. There must be something wrong with the system.

Ask her, had she had any work done?

Dan.

 

[Timmyturtle]

So hertsdrainage what is the cure funny man?

She had boiler changed 18 months ago,no other work since.