hot water going up cold feed into cwsc

[jamesrobinson1000]

the OP said only when bath or basin taps are opened the overflow occurs though ....

 

[jamesrobinson1000]

fair enough. good to know. i just thought that all taps fed from a cold water tank now had to have potable water at cold side due to regs!!

bath, basin can still be run off the tank.at least one
kitchen useally must be off the mains potable water for drinking.

i believe they can be ran from the tank but if they mix in the body at different pressures (ie cold mains and hwsv gravity hot) then they legally require single check's on their supply pipes)

 

[seco services]

yes you should fit check valves.
most times a check valve will restrict the hot gravity

 

[cdel2005]

thanks seco ill let you know what happens
cheers

 

[jamesrobinson1000]

if you fit check valves as suggested, you will get no overflowing but poor flow from the hot side of the tap, even with the hot on on its own. ideally you need balanced supplies to the mixer tap.

 

[seco services]

the OP said only when bath or basin taps are opened the overflow occurs though ....

rare to get it on both taps are they a matching set ?
or where they a cheap set ?

 

[D_Hailsham]

on heating up the water in the cylinder expands a little bit and thus goes back up the cold feed pipe and into the cold water tank.

Hot water rises, not falls. The expansion is taken up by the vent pipe coming out of the top of the cylinder with the HW outlet teed into it

 

[jamesrobinson1000]

D-Hailsham i disagree with you here. water always levels up and the water in the cwsc will be the same height as that in the vent pipe looping over it. when the water is heated and expands it rises back up the cold feed back and a little up the vent pipe, and thus via the cold feed into the cwsc. if it all rose up the vent it would pump over possibly.

 

[seco services]

if it all rose up the vent it would pump over possibly.

how much do you think it expands not that much.

 

[jamesrobinson1000]

i know its not very much. but when it does, some goes up the cold feed and some the vent and the water in the cwsc is the same level as that in the vent pipe (water always levels). its the same principle with the header tank.

 

[kmeeres]

i know its not very much. but when it does, some goes up the cold feed and some the vent and the water in the cwsc is the same level as that in the vent pipe (water always levels). its the same principle with the header tank.

I think it depends on the system meeting "spec".
I have seen flat with boiler in cupboard with expansion tank immediatley above.No headroom so expansion pipe was about 2 ins above rim of tank.
Fine in summer but overpumped in winter when boiler temp was turned up.
Should have been a pressurised system to start with. ?
Shrug, it happens.

 

[jamesrobinson1000]

i agree it happens but it is not good, rapid corrosion of the system, rads mainly, will happen. as you say a sealed system would stop this from happening though. i suppose it happens more with htg on and a higher temp as more expansion of the water will happen.