Cold water tank in loft overflowing

[Fireblade9]

hi this has us a bit baffled our heating systems is cold water tank and little f e tank in the loft immersion cylinder in airing cubard and boiler in kitchen
The problem was the overflow to the cold tank keep dripping so I replaced the ballcock turned mains on watched it fill up and cut off nicely job done
Next day noticed overflow dripping went in loft looked in cold tank ball valve under water so turned isolating valve on mains in ran a few taps so water level dropped left it isolated over night the next day the water level was right up again to the overflow
The cold feed pipe from the bottom of the cold tank goes into bottom of cylinder now that pipe gets hot all the way back up to tank can even see in the tank swirling like it’s back filling with hot but run any hot tap and the cold feed pipe goes ice cold again for about a hour the heats back up
Iv had two plumbers look and are not sure
All taps are mixer type no taps or showers have been changed in last 4 years
Any help or ideas much appreciated I apologise for long post just trying to give as much details

 

[Jim Goodenough]

Is your hot water hotter than usual?

Is your heating system fully pumped? or gravity for hot water circuit and pumped for heating? If it's a gravity system your boiler thermostat could have failed. This will overheat the water.

Alternatively do you use the immersion heater? Has it been left on by mistake (if it's on a high setting and left on it could be expanding your hot water excessively)?

 

[Ric2013]

If you have a hot water cylinder fed from that cold water cistern, the coil in the cylinder could be leaking. If so, the water from your heating system could be pushing into the coil from the small F&E and then passing through the leaking coil and up the cold feed into the cold water storage cistern.

If the ballcock of the F & E is not dripping or the water level in the F & E is lower than the water level in the cold water storage cistern, then I'm probably wrong in the above paragraph.

I like your approach to actually finding the fault, by the way.

 

[Fireblade9]

Is your hot water hotter than usual?

Is your heating system fully pumped? or gravity for hot water circuit and pumped for heating? If it's a gravity system your boiler thermostat could have failed. This will overheat the water.

Alternatively do you use the immersion heater? Has it been left on by mistake (if it's on a high setting and left on it could be expanding your hot water excessively)?

At a guess I think the system is pumped there is a pump near bottom of cylinder

We did leave the immersion heater on for a few weeks straight just so we didn’t have to keep remembering to put hot water on

 

[Fireblade9]

Th

If you have a hot water cylinder fed from that cold water cistern, the coil in the cylinder could be leaking. If so, the water from your heating system could be pushing into the coil from the small F&E and then passing through the leaking coil and up the cold feed into the cold water storage cistern.

If the ballcock of the F & E is not dripping or the water level in the F & E is lower than the water level in the cold water storage cistern, then I'm probably wrong in the above paragraph.

I like your approach to actually finding the fault, by the way.

Thanks

The level in F E tank never moves I put a mark on the side and water level still there weeks later

The two tanks are side by side on a platforms the cold shut off level is a fair bit higher than F E water level

I worry about if it’s over flowing and overflow pipe iced over then the tank would over flow hope that made sense lol

 

[Fireblade9]

At a guess I think the system is pumped there is a pump near bottom of cylinder

We did leave the immersion heater on for a few weeks straight just so we didn’t have to keep remembering to put hot water on

Thinking heating system is pumped
HW gravity also should have mentioned we never switch immersion on just use boiler for hot water

 

[Jim Goodenough]

Is your hot water hotter than usual?

 

[Fireblade9]

Is your hot water hotter than usual?

No just the same it’s not discoloured either
Would any pictures be of any help in loft or cylinder layout

 

[Fireblade9]

No just the same it’s not discoloured either
Would any pictures be of any help in loft or cylinder layout

 

[Fireblade9]

Few pics

 

[Jim Goodenough]

Thanks for the pic, your system is fully pumped - it's great to see the pipes in the cupboard insulated as well!

BTW did you replace the float "ball" when you replaced the ball cock? What I'm getting to is the float "ball" filling with water and opening the valve?

 

[Fireblade9]

Thanks for the pic, your system is fully pumped - it's great to see the pipes in the cupboard insulated as well!

BTW did you replace the float "ball" when you replaced the ball cock? What I'm getting to is the float "ball" filling with water and opening the valve?

I didn’t replace the ball I gave it a good clean and shaked it couldn’t hear any water inside it but there only cheap I’ll get on tomorrow and give that a try

 

[Jim Goodenough]

If there was no water in it that won't be the cause of your overflow problem.

 

[Fireblade9]

If there was no water in it that won't be the cause of your overflow problem.

Also when the cold feed pipe is hot and I go in the loft look in cw tank I can see the swirls like it’s filling up from the bottom Iv filmed it but can’t upload clip yet

 

[Best]

A mixer (shower or tap) can be passing mains cold water into the hot pipework and it will back fill through copper cylinder and up the cylinder feed pipe and into cold tank.
Monobloc mixer tap, like on a kitchen or basin are suspect.
Water passes through them while they are turned off if they have a fault. Even a pin hole of a connection inside the mixer tap between gravity hot & high pressure mains cold will cause an overflow on cwt.