Pump water from cold tank to hot cylinder

[BenRodney]

I have recently had to lower the height of my cold water tank (in the loft), which has resulted in a lower pressure feeding my hot water cylinder, which is on the 1st floor. I have a pumped shower at roughly the same height as the top of the cylinder. This now seems to be pumping water out of the cylinder faster than it can fill, resulting in a very poor showering experience! Is it feasible to install a small pump next to the cylinder to pump water from the cold tank to the cylinder (which would stop my daughter from constantly complaining that she does not have enough time in the shower to wash her hair without having to wait for the cylinder to refill)? If so, would this need to be a positive or negative head pump?

Thanks for any advice!!

 

[HERTS P&D]

Is the float valve on the CWST operating at full flow?

Post some pictures.

Andy

 

[BenRodney]

Pretty sure the float is flowing as fast as it can.... had to drop the tank by about 500mm so there was a very noticeable pressure drop when using a hot tap in the bathroom where the cylinder is. Will post some pics shortly.

 

[terryplumb]

The volume of water in the loft tank shouldn't be any different because the tank has been lowered. Is your issue, with the shower, such that you run out of hot water ( goes cold) or it runs out of water completely?

 

[BenRodney]

I think the problem is that the pump is taking the water out of the hot cylinder faster than gravity can get the cold back into it from the cold tank. When the hot tank level drops, you can hear the pump running dry and only pumping from the cold supply.

 

[terryplumb]

As Andy said ,check the flow of water into the loft tank ,it sounds like it isn't being filled as fast as it is being drained.

 

[Johntheo5]

Is there still water, at least, say 6 inches or so or more?? when the HW cylinder starts running dry?.

 

[BenRodney]

Yeah, there is ample water in the loft cold tank, no where near empty. There is actually 2 x 50 gal tanks and the shower starts drawing air from the HW cylinder after about 7 mins of operation.

 

[terryplumb]

Can you show us pictures of the vent pipe position over the loft tanks.
Where is the hot water take off point to the shower pump from the hot water cylinder.

 

[Johntheo5]

A sketch showing distances from CWSC water level when full and when air starts to be drawn, fom the HW Cylinder, pump inlet etc would be useful, is there a Sussex flange (I think its called) installed in HW cyl?