Combi Boiler and using cold water storage tank

[Lesc]

I have a 2 bed flat in a block of flats and plan for a separate shower and bath. I'm replacing the existing vented system with a Worcester Combi and have had quotes from 2 gas engineers.

I asked about any problems with showering if there is simultaneous use of, say, the washing machine and dishwasher. I was told that the shower may be affected because of the heavy demand upon the mains supply - even if they are only set up to use cold fill.

What I cannot understand is why everything has to come from the mains and we cannot utilise water in the storage tank on the roof. Why can't the mains supply provide for drinking water and hot water via the combi and allow the cold supplies to the appliances and toilets to be taken from the storage tank on the roof (as seemed to be the case with the old heating system)?

can you advise

 

[Chalked]

Mains pressure is needed to operate the flow switch. The flow issue is not down to the main not supplying enough, its the boiler that can only supply a finite amount .

 

[Ermintrude]

?? Thought it was the problem with unbalanced hot and cold. What pressure and flow do you have in flat? If it's a big block you may be lucky enough to have a Boosted cold water supply

 

[AWheating]

if your cold water supply if quite good then dont worry, you could just not put the washing machine on before you take a shower?

 

[diamondgas]

What I cannot understand is why everything has to come from the mains and we cannot utilise water in the storage tank on the roof. Why can't the mains supply provide for drinking water and hot water via the combi and allow the cold supplies to the appliances and toilets to be taken from the storage tank on the roof (as seemed to be the case with the old heating system)?
can you advise

There's no reason why you can't do as you say in my opinion! Nothing stopping you supplying the toilets and washing machine from the header!

 

[Ermintrude]

Few houses do but cistern takes an age to fill.,

 

[Lesc]

Hi Ermintrude - you helped solve an earlier issue for me.

The only tests they have done are turning on the cold tap. Both said it appears ok. One placed thumb over tap saying it seems fine and the other said that he should do a pressure test. I ran the tap for one minute and got 17 litres (if I remember correctly).

 

[kris]

Hi lesc remember that even putting a header tank to fill toilets still needs mains to fill the tank so whether its mains filling the wc the tank still needs to fill so the header is not really much use to be honest,

 

[Lesc]

I understand. But it's not likely to be me in the shower who will turn on one of the dishwasher/washing machine.
i suppose that what I am wondering is why two engineers arrived at the same conclusion - everything off the mains even when there is a cold water storage. Indeed, why can't the cold supply from the Tandy serve all the non- drinking outlets such as cold bath taps?

 

[Ermintrude]

I would ask for a dynamic pressure test. Basically attach pressure gauge and open another cold tap. 17lpm isn't brilliant tbh ! I would be looking at an accumulator or open vent with a kick bum booster set.

 

[Lesc]

There is a large tank on the roof serving the 30 flats in the block. I guess this is filled and held in reserve until there is a demand (demand at times which may be greater than can be directly met by mains alone). If I draw upon this second source for my non-drinking cold supply will this help with running a shower, washing machine etc simultaneously? (I'm sorry if my naïvety on this makes me seem stupid!).

 

[Lesc]

I don't know about these but will ask the engineer? Should one or both of these be included now or wait until after the install and testing?

 

[stevetheplumber]

no reason a combi cant run from a tank its just how high the tank needs to be which is usually the problem
we fitted a combi in a flat and teed of the suppy to a electric shower asuming it to be mains fed, it wasnt till we went back for some other work we realized it was tank fed ,as the tank was 50 ft above we all agreed as it was working we would leave it

 

[Ermintrude]

Yes most flombays work on a turbine so it's flow rate opposed to pressure, but the phex will need the pressure to get water through narrow waterways.

 

[Lesc]

Can a combi and kitchen/drinking cold run from the mains but all other cold supplies run from the tank? And, if this the case, would it help with flow and pressure limitations?

 

[AWheating]

Wow a lot of expensive suggestions, if you have OCD and can't shower without the washing machine or other taps on, then fit some flow restrictors on the fixtures. 17lpm is plenty for a decent shower from a combi.

 

[stevetheplumber]

Can a combi and kitchen/drinking cold run from the mains but all other cold supplies run from the tank? And, if this the case, would it help with flow and pressure limitations?

you can provided there are no mixer taps and a shower is a mixer taps as such

 

[stevetheplumber]

Yes most flombays work on a turbine so it's flow rate opposed to pressure, but the phex will need the pressure to get water through narrow waterways.

no its pressure that drives the turbine the hole the water passes through is microscopic its the pressure on the turbine blades