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Question DetailsAsked on 10/29/2015

I can hear my hot water tank running. There is no water running anywhere. Water comes out lukewarm when turned on.

I can hear the hot water heater heating up the water in the tank. There is no water leaking anywhere. The water pressure throughout the house is normal. However, when I do turn on the hot water it only gets warm not hot. The pilot and everything is normal. The temperature hasn't been moved.

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1 Answer


Assuming here you have a conventional, not on-demand water heater. If on-demand unit, then presumably a thermostat, sensor, or control has failed, or it has become plugged because you have not been flushing/cleaning it as often as your should. Ditto (except for the cleaning part) if you have combined hydronic/steam boiler and domestic hot water system, where the boiler provides the heat for all the hot water uses in the house. Call technician.

1) carefully, so you don't burn your hand - check the temperature of the hot pipe coming out the tank (usually on top) - be sure not to touch the potentially VERY hot exhaust flue duct. Obviously one will be cold or room temp (incoming water) - the other should be hot to the touch - too hot to comfortably hold onto for any period of time, because it is about 120-140 degrees. If it is hot, then you may have a partial blockage in the outlet from the tank - buildup of minerals or a floating piece of deteriorated interior plastic fill tubing, which some brands have had issues with. However, in this case, the water coming out of a faucet turned to full hot would be initially hot (after the pipes heat up for a few seconds), just lower flow rate than normal, but because of the lower flow rate would result in less available hot water volume in mixed cold/hot applications. But would initially be hot, since you said good pressure (which I presume to mean good flow, not pressure). If flow out hot tub (so checking full flow capacity) faucet is same as from cold, then this scenario is highly unlikely the problem.

2) If neither pipe coming out of the tank is hot, then possibly sediment in the bottom of tank built up around the thermostat probe and keeping it hotter than the water - sediment should be flushed yearly at servicing, though would normally take a good several years or decades of buildup to bury the probe in sediment. Go to #4 if this has not been done in some years.

3) If top pipe is only lukewarm and electric heater, possibly one element (many heaters have 2) has burned out. Depending on how long the tank has sat, would normally (after a long period without hot water use - say an hour or two or more) start off full hot but not have much hot water capacity (slow reheating) so hot flow would cool off fast. Generally, except for very low Btu heaters, one element will heat the tank to normal temp in an hour or two - just can't heat fadt enough to provide recovery as water is used, so typically starts off full hot but drops to lukewarm pretty fast.

4) If not hot at all, but burner is firing after hot water is used for awhile, then has to be a thermostat issue. Try turning it back to low or vacation, then up 10 degrees or so above where it was - sometimes as they get older they get a bias in them, so have to be adjusted (usually hotter) to get the same temp water. If not certain about how hot the tank water is getting, CAREFULLY (use gloves, goggles or faceshield, and rag draped around faucet in case it leaks) empty a gallon or two of hot water from the drain valve into a bucket - and measure the temperature of it. If not hot enough, try adjusting thermostat dial up then test again in a couple of hours. This is also how you flush sediment - flush till water runs clear. If quite dirty at first, you may have to connect a hose to flush 5-20 gallons to get it to come clean.

5) If you have high-efficiency newer model with electric heat pump on top like this picture - where it shows 4 brands of heat pump water heater -

could be the heat pump thermostat has malfunctioned, causing it to think it can provide all the heat you need when you actually need heating element/burner heating. Of course, if the burner is firing (for non-electric unit) that is clearly not the case.

6) If you have a constant hot water system - where the hot water is almost instantaneous at the faucet because you have a recircuylating pump, perhaps the pump has failed - in that case, hot water would come, just might take a few seconds to as much as 30-60 seconds for the hot water to make it to the faucet if you are in cold weather and/or hot pipes are in an unheated basement or crawlspace and the run is long to the faucet.

If not up to doing these measures or going through them does not answer the issue, then call a Plumber.

Answered 4 years ago by LCD

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