Changing boiler for combi, worried about flow on shower

[richuk]

Hi
I currently have a standard old (nearly 20yrs) Potterton boiler with tanks in the loft and cylinder in the cupboard.

I run a Mira Event XS power shower off this, I believe to be 14l/min and it gives very high flow rates.

I am looking to change my boiler for a Vaillant 937 and wondered what the flow would be like to the shower (changing the mira for a mixer to remove the pump). Will there be as much flow? I notice many retailers advertise flow rates at so different temperatures and presume the mira flows at the cylinder temp at 14l/min if you wanted it to !

The main reason for this request is that my wife loves the high flow of the shower and would kill me if I changed the whole system and the shower turned out to be not as good !

Thanks

Richard

 

[leakydave]

what is your flow rate from your cold water main? Your shower output froma combi would be similar, if a little less, to this. I recommend a thermostatic shower, so when a loo is flushed when the shower is running, the shower doesnt get colder/hotter

 

[Doctor Drivel]

what is your flow rate from your cold water main? Your shower output froma combi would be similar, if a little less, to this. I recommend a thermostatic shower, so when a loo is flushed when the shower is running, the shower doesnt get colder/hotter

Don't get a thermostatic, The combi regulates the DHW temperature. Get a combi compatible mixer with an integral pressure equalisation valve.

To stop one outlet robbing another, the combi need its own dedicated cold feed from the stoptap, preferably in 22mm even if the cold mains pipe is 15mm. The 22mm has far less restrictions to flow and pressure. Take the cold for the shower off this pipe just before the combi - any pressure fluctuations around the combi will then acts equally on the cold and hot of the shower. Then the cold taps will all be on one leg from the stoptap. Also, replace the stoptap to a full-bore tap.

If still problems then put flow regulators on the offending appliances, like say a toilet, which doesn't need to fill fast. Regulators are available from http://www.bes.co.uk

Shower is king in a mains pressure water system. Everything must revolve around the shower and ensure the shower takes the flow and pressure.

DO NOT have a 15mm cold mains pipe snaking around the house and the combi teed off this as if it is just a basin. Pipe it up right!!!!

 

[richuk]

Thanks Dave and Doctor Drivel.

I've measured the flow from the cold tap (off the water main) and its about 12l/min, although the main stock cock isnt fully on and is jammed, so I'm sure the flow rate once this is fixed will be better.

I was thinking of putting the new boiler in the integral garage to my house, but a pipe from the main water stopcock to there is round the kitchen, up the boxed out pipe section, along the landing into the bedroom and back down into the garage !

Back to my original question, do you feel that the flow rate would be similar to the power shower I currently have?

Thanks
Richard