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Question DetailsAsked on 1/21/2015

what causes low hot water pressure cold water pressure id ok

hot water pressure is low no work has been done just seemed to occur

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1 Answer


By "pressure" I presume you mean how hard it comes out of the faucet or showerhead - which is usually actually a volume issue not pressure as such, even though it exhibits as a reduced or meager "pressure" coming out of the head at point of use.
0) I am assuming this is true at all points of use in the house - if only at one faucet, then that faucet/valve is suspect, most commonly with single-handle faucets and shower mixer valves, where either the constant-temperature feature fails (with some fancier shower mixing valves), or where a seat or seal fails and partly blocks the water passage. Normally this sort of problem can be fixed by installing a rebuild kit in the valve/faucet. If at a showerhead but tub spout (if shower/tub) puts out plenty of hot water flow, then the showerhead would be the suspect.
1) Most common cause is probably a blockage of the intake tube in the hot water heater - in some cases (though most of the units where this was a recall issue have been replaced by now) due to the plastic cold water tube inside the water heater breaking apart due to the heat and floating up in the tank and partly blocking the outlet to the hot water pipes. 2) If gradual loss of pressure over mohths or years, can be due to buildup of scale (iron and/or lime deposits) in the pipe. Occasionally, a piece of this scale can break loose and partly clog a pipe also, causing an instantaneous loss of flow rate for all points of use downstream from that clog. 3) If you have a combined hot water system (same boiler heats domestic hot water and hydronic (circulating hot water) household heat, then the temperature control/mixing valve that regulates the mixing of cold water with the near-boiling hot water in the holding tank to provide the 120-130 degree domestic hot water may have failed. 4) If you have a hot water circulating system to provide near-instant hot water when you turn on the faucet, if the pump stops then it acts as a barrier to flow, and the amount of hot water that makes it to point of use can drop anywhere from nominally to quite dramatically, depending on type of pump. 5) In rare cases in houses with high water pressure and for some reason they did not install a whole-house pressure regulator to limit that, there is a pressure regulating valve installed at the inlet to the water heater to limit the pressure it sees, which can reduce the pressure in the hot water system if it goes bad. Also, in some cases, plumbers install pressure relief or expansion tanks in accordance with new code reequirements, to prevent overpressure in the pipes from the hot water heating when there is no demand, but incorrectly put in a tank which has a factory-installed inlet pressure control valve, which can cause a pressure drop in the hot water piping when it goes bad. In any case, sounds like you need a Plumber. This does not sound like a fun one - probably going to take a couple of disconnections and flow tests to see where the blockage is, then of course the repair, which could take a total of a couple hours or more - so you might be pleseantly surprised, but I would be prepared for more than a minimum service charge. I would not be surprised to see a $200-400 bill, possibly more by a couple of hundred or so if a constant hot water system circulating pump has to be replaced.

Answered 4 years ago by LCD

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