Mains pressure systems (combi, thermal stores & unvented cylinders) have to be fitted properly, not having one 15mm cold mains pipe snaking around the house with the combi, or unvented cylinder, teed off it like it was just another sanitary appliance.
Shower is king, all pressure and flow must be
prioritized for the shower. Water takes the line of least resistance, make the shower hot and cold the least resistance in the system. It needs:
- Have its own 22mm cold feed from the stopcock to the combi even if the mains pipe is 15mm
- A full-bore stopcock
- Split the combi feed and cold outlets at the stopcock. Fit a tee for all cold outlets, except the shower. This can be 15mm in most cases.
- tee off the combi's cold feed, for the shower cold supply, just before the combi. Any flow pressure fluctuation around the combi will act of the hot and cold of the shower.
- have a dedicated hot pipe from the combi for only the shower.
- have the hot & cold outlets and taps on flow regulators (they are combined flow regulators and isolation valves) - you do not need firehose flow and pressure on bathroom basin taps, kitchen taps, toilet, dishwasher, etc.
- one flow regulator can do the dishwasher & washing machine which can get away with 6 litres per/min. In fact one regulator can do all the cold outlets, except the shower and bath, which should not be regulated.
- the shower hot and cold pipes should have no tees off these pipes. The shower hot & cold needs dedicated pipes.
- no flow regulators on the shower hot and cold.
- Use the equiv to Raindance shower heads, that consume less water.
Doing it this way it auto balances the hot & cold system to a large degree, the flow regulators on the the outlets fine tune the balancing, so no huge cold slugs while in the shower when the kitchen taps are turned on. This applies to
all mains pressure systems.
Combined Flow regulator/isolator tap. A flow cartridge is inserted into the side - 6 litres/min, 2.5 litres, etc. A kitchen only needs 6 or 8 litres/min on hot and cold (I find it fine with 6), dishwasher/washing machine only 4 litres/min (a minute or so longer in the wash cycle is neither here or there), toilets can be 4 litres/min. 2.5 litres/min in a small downstairs toilet hand basin. Fit none on the showers.
Part number 17527 plus flow cartridges from 2.5 litres/min to 15.
https://www.bes.co.uk/flow-regulator-ball-valve-cp961-15mm-17527