Hot water being back flowing into Cold water tank

[Mark_James]

Any advice would be extremely appreciated. I have an indirect heating system. A few days ago the large cold water tank overflow started to leak. Given that I had the ball-cock replaced 6 months ago I kinda knew it was not the problem - it was not.


When the water is being heated on its own it is raising the water level in the large cold water tank up to a point where it overflows down the pipe at the roof eves.


This happens over a period of a 90 mins (water is only heated for 20 mins). Having looked in the tank I can see that water is being backfilling the large cold water tank not via the open vent pipe but the pipe at the bottom of the tank where the cold water should flow to the Cylinder.


When the hot water is off (not heating water) the large cold water tank level remains as it should.


Any ideas why this is happening???? I have had no new taps or mixers installed and this has only happened (as far as I know) in the past few days

 

[Chuck]

Sorry previous answer assumed unvented system not vented.

Has the vent pipe been blocked perhaps?

By the 'large cold water tank' are you referring to the central heating expansion tank, which will probably be full of rusty water, or the main cold water tank, which will partially empty when you run a bath?

C.

 

[Mark_James]

Thanks but aren't g3 installments for unvented system. Mine is vented.

 

[Sedgy40]

Sounds like the system needs balancing.....

 

[Tonycane]

gravity hot water System?

 

[Mark_James]

Sounds like the system needs balancing...

Any ideas how?

 

[Mark_James]

gravity hot water System?

I think so. Water tank in loft, cylinder on first floor, boiler on ground

 

[moonlight]

Have you tried blowing down the vent pipe? If it's not blocked, you should get movement from the cold feed outlet.

 

[Mark_James]

Have not tried that. What could block it??

On line seems to point to cylinder but I hope it's not that

 

[Mark_James]

Sorry previous answer assumed unvented system not vented.

Has the vent pipe been blocked perhaps?

By the 'large cold water tank' are you referring to the central heating expansion tank, which will probably be full of rusty water, or the main cold water tank, which will partially empty when you run a bath?

C.

Main cold water tank

 

[Sedgy40]

Have not tried that. What could block it??

On line seems to point to cylinder but I hope it's not that

No lid on water tank in loft

 

[Tonycane]

presuming you have an open vented heating system, isolate the cold feed to the f+e, if the water starts disappearing this could point to the coil in the cylinder splitting

 

[Mark_James]

Thanks everyone

Yes it's a gravity system

It's the main cold water tank ( not the heating One)

I have not tried to blow down the vent pipe. What could be blocking it?

 

[Mark_James]

No lid on water tank in loft

Both have lids so may not be that

 

[Sedgy40]

Thanks everyone

Yes it's a gravity system

It's the main cold water tank ( not the heating One)

I have not tried to blow down the vent pipe. What could be blocking it?

Do you have immersion heaters in the cylinder?
Post a pic if poss

 

[Mark_James]

Yes but never have it on

 

[moonlight]

Sorry wasn't reading thread properly . If hot water is coming back up through the cold feed. It most likely is your cylinder, especially if the water level of your f&E tank is lower than your cold water storage tank.

 

[Mark_James]

Which it is, the heating is no problem. Only when the hot water is heated

 

[Tonycane]

so, f+e tank has more head pressure, so heating water is able so act against the hot water system head pressure, this will fill your cylinder via the faulty coil, this then travels back up the feed pipe and back in to your cold water storage tank. shine a torch thru the water at the bottom feed pipe, you will see the hot water if that makes sense

 

[Mark_James]

It does but I don't nor have evey had them on together. Always seperate