Hot water being back flowing into Cold water tank

[Chris Dodds]

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

 

[Dan Robinson]

Hot water cylinder is fecked.

 

[Chris Dodds]

Cheers Dan Robinson any idea how long it will "last" before it becomes unusable?

 

[Dan Robinson]

Well, I would be double checking that's the problem first by isolating both the heating and the hot water systems and draining the cylinder and seeing if the heating drains too.


Then, if proven to be the problem, change the cylinder as asap.

 

[Chris Dodds]

that beyond me mate - would not know where to start to do that

 

[Dan Robinson]

Might be worth posting your location and see if one of the regular posters are nearby. Changing a cylinder is not a massive job, but if you've eliminated mixers and showers, there aren't many other options. One of my guys is attending an identical problem on Tuesday, last time it was the ball valve, but this time it's probably the cylinder.... And in this lady's case it's not going to be cheap as it's a big house and a mahooooosive cylinder.

 

[Chris Dodds]

Thanks again, I am based in Newcastle Upon Tyne - Denton Burn (if I need to post it somewhere else please let me know)

 

[oilhead]

How far below the overflow is the level when cold? If it is high, then expansion whilst heating water may be overflowing. If it does not happen when cold, then I would first adjust the ball valve to lower the cold level and see if the problem goes away.

 

[Chris Dodds]

thanks oilhead it is about 5/6 inches when "normal". Water is being backfilling the large cold water tank at the pipe at the bottom of the tank where the cold water should flow to the Cylindernot and not via the open vent pipe

 

[alan999]

It is back filling quite fast. Does the feed and expansion tank keep topping itself up while this happens

 

[Chris Dodds]

It only back fills when the hot water is turned off and it is not used straight away. If it is not used over 90 - 120 mins it starts to raise and come over the over fill level out the over flow pipe. 5his is only in the large cold water tank. The smaller tank (full of discoloured water - the one that gets pushed round the heating) is uneffected.

 

[gassymark]

Just a question do you have a thermal store ?

 

[Chris Dodds]

Nope

 

[Chris Dodds]

I have a imersion back up (in case of boiler brakedown) but I have never used it

 

[gassymark]

probably Dans right coil split in cylinder I take it the f&e tank is higher in the loft than the dhw header tank check the f&e tank overflow is not connected to the dhw over flow and backfilling from that.
Cheers mark