Attic tank and Combi

LimerickGray

If you like puzzles you’ll love this.  

My combi boiler supplies hot water to my shower.  The cold water to the shower is mains.  All toilets and sinks everywhere are mains.  The tank in attic is not used or connected to anything

The shower is a bar temperature mixer type and not pumped. Max temp is set at 40deg.  

Pressure can be a bit low.  

If I set combi to heat water at above 40deg then the shower will call for cold water to balance back to 40deg.  This causes a drop in shower pressure as mains cold is being used while hot being supplied to shower

Would it be possible to allow the shower to take hot from combi and cold from the storage tank in attic instead?   

The issue I see with that is the attic tank water level will drop and then call for mains cold to fill it.  This is back to same problem as the hot pressure will drop

Is there a delay fill valve for attic tank?   A fill valve that doesn’t call for mains water until tank is very low. 

if I lived alone I could manually fill the attic tank when empty by putting a gate valve on the inlet but it needs to be family friendly.

I’ve seen delay fill cistern valves but I need a very big delay.

Sleeper12

Everything is plumbed incorrectly. The only thing that should be connected to the mains is the cold at the kitchen sink and the inlet to the cold water tank in the attic.

Cold water and water going to the combi should both come from the attic storage tank. Both hot and cold should be Pumped. This is best practice

LimerickGray

Not much I can do about that now really lol

is my plan feasible

Shauna677

https://www.boards.ie/discussion/comment/119619340#Comment_119619340

Hi, i have a vissmann combi boiler that works directly off the mains, actually everything in the house works off the mains as i have no cold water tank in the attic, house is built on a slope so water pressure is mighty, only time. I have an issue is if the water is fillling in the bath or the kitchen sink, the water pressure in the shower is not as good or vice versa.

LimerickGray

My combi is fine. Except if the heated water is too for and then I need to add cold. That cold is also mains and it drops the hot pressure

LimerickGray

What temperature is your cold water output set at? I presume this would be too hot to shower in. The cold needed to reduce that combi hot is mains too. Does that reduce the hot pressure as well as temperature

John.G

Looking at it from mains only supply, it doesn't matter whether you mix very hot combi water with cold mains or reduce the combi hot water to your showering temperature with no cold mains required because both hot & cold are from the same mains supply.

If you supply the cold by gravity from the CWST then the shower flow will reduce drastically as the mixing will take place at the gravity fed head and you may also have to install a dedicated PRV set to 1/1.5 bar on the shower cold supply to allow the thermostatic mixer to work. You will get a far better flow with the reduced mains pressure, as is.

If the mains pressure is only a problem when used else where with shower in use, maybe possible to supply some from the CWST fitted with that delayed filler, a normal ball cock in any event does not fill at full rate if no long drawn out draw off of cold water.

LimerickGray

https://www.boards.ie/discussion/comment/119619682#Comment_119619682

thanks for the advise

I actually had a fault with this combi boiler and they sent out someone from Ideal today. Fault was nothing to do my above issue but I got talking.

He said it is quite common when folk install a combi and remove the loft tag and immersion. He is not aware of any delay action float valves that would prevent the tank from filling instantly. He said a PRV on the entry to the float valve might help as there is no need for it to fill quickly and that might be enough to stop the combi hot pressure from dropping.

We tried it with taps here. ran the shower at 50C and slightly opened a cold mains tap and no obvious effect on hot coni pressure. Obviously flushing a toilet would kill the hot pressure.