can I add pump at water main entry point if my central heating is still gravity feed?

[Sup9]

I bought the house with gravity system for both hot water and central heating (two water tanks in loft). I then have am unvented cylinder installed in the hope of better pressure. It was unfortunately marginally better so I' m thinking of adding a Grundfos scala 2 pump at the water main entry point. I still have the old boiler ( 20yrs+) and heating loop is vented, not sure if I can add the pump for added pressure with the existing system or I have to change the boiler and have the whole system unvented at the same time?

I'm looking to have good pressure when only one shower is in use but useable pressure when two in use, and will be adding a water softener so I'm thinking of the Scala 2 for the power required.

 

[Gasguru]

The domestic water and heating system are separate....and by the sounds of it the large water cistern is now redundant.

You can't pump more than 12 litres/min directly from the mains supply...water company regs.
If you want to pump more than that you will need a break tank...but AFAIR that requires approval first, and this would be the last resort.

Firstly, check the static water pressure ie. the pressure in the main service pipe from the road with no water flowing.
Then check the pressure at different water flowrates eg. at 5, 10, 15, 20 etc litres/min.
Ideally you need to connect a gauge as close as possible to the indoor stopcock..perhaps utilising the cold washing machine valve.
Until that is done you can't make a sensible decision...and clearly this wasn't done before an unvented cylinder was installed.

 

[fixitflav]

I still have the old boiler ( 20yrs+) and heating loop is vented, not sure if I can add the pump for added pressure with the existing system or I have to change the boiler and have the whole system unvented at the same time?

No, you don't. The boiler circuit sends hot water through the primary coil in the HW tank, and can be vented or pressurised. There's pros and cons of each, but my preference is vented i.e. leave it as is. It's independent of the water into the tank from the mains and out to the taps.

 

[fixitflav]

and by the sounds of it the large water cistern is now redundant.

I suppose he could keep the CW tank, to supply all the cold taps bar the kitchen. Then at least he has some storage in event of mains outage. He hasn't said he has a (mixer-type) shower, but if he does the cold to that would need to be be direct from the main, obviously.

 

[oldbutnotdead]

If the incoming water pressure isn't up to it, could one reconnect the old header tank to the supply to the unvented cylinder (obv disconnecting the rising main supply) & stick the pump on the output of the cylinder (or even the supply pipe from the header tank to the cylinder). Seems it would be technically feasable, not sure how many bylaws it would breach & might have to look at pipe sizes (which also should have been done as part of the unvented fit)

 

[Gasguru]

Not a good idea to drink Category 2 water ie. warm water from a cistern in the roof...lofts easily get to 40 degrees in the summer.