Combi Cold Water Design

[diy_darren]

I thought that a combi boiler took a cold feed in and then had a cold feed out so all hot/cold water (for taps) passed through it. Am I mistaken, or do different manufacturers do it differently?

I was looking at the Vaillant 838 install manual and noticed they only have 5 connections; CH flow, hot, gas, cold, CH return (plus the filling loop).

If the cold taps in the house are fed directly by the incoming mains water do I need to give any consideration to where on that circuit the boiler gets it's feed? Should the boiler be the first connection off the incoming mains, or does it not make any difference?

Thanks.

 

[BigBurner]

If the cold taps in the house are fed directly by the incoming mains water do I need to give any consideration to where on that circuit the boiler gets it's feed? Should the boiler be the first connection off the incoming mains, or does it not make any difference?

Thanks.

Fit a full bore maintap. From this take 22mm, even if a 15mm main pipe, directly to the combi. All the cold outlets will be on one leg then. Nothing teed off this pipe - except the cold to the shower(s) just before the combi. Take the hot for the shower back to the combi and have a mixer with an integrated pressure equalising valve inside - or one external. Put isolation valves on each appliance and tap and throttle back to suit. A dishwasher does not need full flow, neither does a basin or toilet. Balance the system up.

 

[gas4you]

In practice no difference although theory may say different.

If you are concerned about balanced pressures fit a pressure reducing valve just after your cold mains stop cock and set it to about 0.5 bar leass than your incoming mains pressure.