Hello,
I have removed a washbasin with separate hot and cold water taps from an ensuite bathroom in my mother-in-law's bungalow and fitted a new basin with a mixer tap. When I connected everything up and tried the tap I got hot water but no cold. However, the cold water supply pipe got warm suggesting hot water was passing through the mixer and down the cold supply. It turns out the hot water is not supplied from a tank (well I knew that) but is an "on demand system", presumably pumped. However, the cold supply to this basin is from a cold water tank, situated, I think, just above the ensuite bathroom. I assume therefore that the hot water pressure is much higher than the cold (it certainly looks like it). Do I have to fit a pressure reducing valve to the hot supply (rather than just partly closing the isolating valve)? Do I have to fit non-return valves anywhere? Alas, the cold supply from the tank to the WC cistern is now very slow. Have I got an air lock in there now and how can I get rid of it? Thanks for any advice. Fergus

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Originally Posted by FergusD

Hello,
I have removed a washbasin with separate hot and cold water taps from an ensuite bathroom in my mother-in-law's bungalow and fitted a new basin with a mixer tap. When I connected everything up and tried the tap I got hot water but no cold. However, the cold water supply pipe got warm suggesting hot water was passing through the mixer and down the cold supply. It turns out the hot water is not supplied from a tank (well I knew that) but is an "on demand system", presumably pumped. However, the cold supply to this basin is from a cold water tank, situated, I think, just above the ensuite bathroom. I assume therefore that the hot water pressure is much higher than the cold (it certainly looks like it). Do I have to fit a pressure reducing valve to the hot supply (rather than just partly closing the isolating valve)? Do I have to fit non-return valves anywhere? Alas, the cold supply from the tank to the WC cistern is now very slow. Have I got an air lock in there now and how can I get rid of it? Thanks for any advice. Fergus

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Hi Fergus,
Since you just got through installing the valve you must know The brand name and model #. Would you care to share them with me? Since a tankless is a water heater and not a pump the hot and cold pressure should be the same. My guess, at this point, would be that you disturbed some crud in the pipes that has lodged in the cartridge cold water inlet ports.
Shut off the water and take the valve apart. Check the cartridge inlet ports for trash or blockage. Now place a pan over the open valve to prevent splash and turn on the water and flush out the supply lines. There should be a strong stream. Reassemble and try again. Good luck, Tom