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I had my bathroom refurbished a while ago. Ever since, when I have my kitchen taps (downstairs) both hot and cold on fully, then turn off the hot tap, cold comes out much faster. Any clues as to why? I mentioned this to the plumber who did the job, who said he didn't know why and left it at that. Is there anything I can do to resolve this problem? I also don't think the pressure is as good in my bath taps as it used to be. I did have a powerful shower installed.

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  • Can you define what you mean by "faster"? Is the overall water flow higher/faster than when more are turned on or does it remains the same essentially doubling the cold when the hot is turned off? Are you on city or well water? House, apartment, bungalow? How many stories and where are you experiencing this?
    – Jason
    Jul 28, 2013 at 13:46
  • Is this a washer-less or 1 handle faucet?
    – Ed Beal
    Jul 6, 2022 at 19:13

2 Answers 2

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In some systems, hot water comes from a first-floor tank pressurised by a cold-water header-tank in the loft. This header-tank also supplies the cold water taps. Part of the reason for this is that mains water supply to the house is at a high pressure, the header tank provides a lower and more constant pressure that is more suitable for household taps and appliances.

Normally the cold water tank has separate outlets for each to prevent the sort of problems you describe. If your system instead uses a single low-pressure feed pipe to both cold taps and to the hot-water cylinder, that might explain the symptoms.

Since you say 'tap' and not 'faucet' I suspect you may live in a locale where the above applies.

A better plumber might be able to advise what can be done to improve the situation.

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The norm is 1/2" to get better hot water pressure. I advise to change the hot water supply lines and valves coming from the heater to the faucets to 3/4". Also when water is heated, the calcium will concentrate and attach to copper & brass; plastic PEX pipes will help solve some of the calcium problems. Tankless heaters are very susceptible to calcium & mineral buildup within the coils. If you want a problem free flow of water, you can install a flush connection and circulate vinegar once a year through the pipes & valves using a large bucket and an electric water pump, that will need to run for about 30 minutes.

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  • Enlarging the hot water lines would be foolish. Everyone thinks "bigger is better" but this ignores the inventory of water sitting in the hot water pipe. You know it well: it's the cold water that comes out of the hot faucet for the first 20 seconds, and you have to wait, wait, wait. Well, if you enlarge the pipe 225% (1/2 to 3/4), you increase the wait 225% also. So now 45 seconds. Nice job fixing it! Jul 6, 2022 at 20:10

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