Gravity fed CWS with no vent pipe conundrum

[Panopoly]

I want to have a shower installed but this requires a bigger supply of hot water and an increase in water pressure. The simple solution would be to install a larger vented hot water cylinder with a pump.
I live in an 1970 block of 62 flats. The plumbing and electrics were put in and sealed in concrete. The bathroom is gravity fed from a header tank at the top of the building, 2 floors above me. The problem is that there is no vent pipe or way of installing one. Is it possible to install an electric shower or power shower directly from a gravity fed CWS? Or is it feasible to have a unvented hot water cylinder with a pump supplied from the gravity fed CWS?​

In the bathroom, hot water is currently provided by a very old flat back Heatrae hot water heater with ballcock and thermostat. (see photos) The overflow from the tank has plastic pipes that run into the bath overflow.

The flow rate from the cold water supply is 12 litres per minute and 6 litres per minute for the hot water supply.
The bottom of the HW heater is 60cm above the taps and 150cms from the top.​

The hot water heater is only 60 litres in size and will slow to a dribble after about 3-4 minutes until it is replenished by the cold supply. The refilling of the hot water tank from the CWS is slower than the toilet system refilling!

I know I could run an unvented system from the mains in the kitchen but this is at the other end of the flat it would require major renovation work to chase pipework into walls and floors.

Is there a solution to run a shower using the gravity fed CWS and if not can anyone suggest a suitable replacement hot water cylinder for a bath minus the shower?

I've added some pictures of the existing water heater plus the pictures of existing supply pipework and overflows. Pic 1 Old Heatrea Hot water tank. Pic 2 CWS and waste pipes (bath discharge is separate from main waste (sink and toilet) pic Basin bath and overflow pipes (plastic plus basin and bath waste pipes. pic 4 CWS to HW tank and overflow pipes and HW tank overflow and toilet overflow into bath overflow (plastic) pic 5 CWS to HW tank and HW tank overflow pic 6 HW tank overflow to Bath overflow (plastic) and HW supply from tank to bath and basin (copper colour pipe)

Thanks in advance for any constructive solutions/ideas.

​

 

[Gasguru]

Have you considered a thermal store cylinder?

The safety requirements are not as stringent as an unvented cylinder..just a conventional overflow into your existing bath overflow/warning setup or into a stack via a tundish/HepVo trap.
The roof cistern cold feed would continue to supply your bathroom and shower whilst also feeding the cylinder DHW calorifier to provide hot. You would need to check with the manufacturer what pressure drop through the cylinder coil is likely since they are normally fed with high pressure mains water.

I would avoid pumps at all costs...you are bound to have noise complaints from neighbours to the freeholder...I've been there.
Pumping the roof cistern could be problematic especially with rusty pipework and if not restricted could lead to water starvation in other flats.

 

[Panopoly]

Hi Gasguru

Yes someone else mentioned using a thermal store cylinder. It sounds like a possible option though I'm finding it hard to source one that isn't mains fed. The manufactures I've spoken too are a little warry of saying yes to using a product described as mains fed on a gravity fed system - probably to cover themselves in the event of the pressure being insufficient. I've also been looking at Triton showers such as the T90XR https://www.tritonshowers.co.uk/electric-showers/t90xr-pumped-electric-shower.html and running that directly off the CWS bypassing any connection to a cylinder. Anyone know why it's recommended not to have other cold water draw-offs between the cistern and the unit, nor supply water to any other tap or fitting at a lower level when installing an electric shower like this? In a solo property I guess there might be a risk of water being drawn off elsewhere causing depletion of the tank supply and lowering the water pressure sufficiently to damage the heating element or pump in the shower, but with a very large plunge pool sized water tank supplying a whole building I can't see this being problematic.