Q:
My 50-gal. Mor-Flo water heater supplies both my domestic system and my heat-recovery ventilator (HRV). The water heater’s temperature is set at 170° F, and the domestic water goes through a mix valve that cools the water to 120° F. The hot-water outlet has two air-bubble removers— a large one near the water heater and a smaller one near the HRV. All of the water goes through a water softener installed one year ago. I have a drilled well with pressure set at 20 psi to 40 psi on/off. The problem is that whenever a tap in the house is turned on, the water heater groans and rumbles loudly. The water-heater manufacturer thought that because I had hard water, scale was building up and cracking, causing the noise. But there has been no improvement since the water softener was installed. How do I stop the noise?
Steve Costain, Nottingham, NH
A:
Peter Hemp, a plumbing contractor in Albany, California, replies: Pipes filled with water transmit noise efficiently, so it won’t be easy to find the origin of the noise. However, I once had a similar noise problem with a hot-water system, and it turned out to be the gate valve at the inlet to the water heater. The gate inside the valve would flutter as water passed into the tank, causing a lot of noise heard throughout the building. I replaced all the gate valves in that system with quality, full-port ball valves, which solved the problem.
There are lots of possibilities, though. If you operated your water heater for a while prior to installing the water softener, any scale buildup could still be in your tank and could still be making noise. Usually scale buildup causes loud popping, cracking and rumbling noises.
Draining and flushing the water heater could stop the noise. (For more on water-heater maintenance, see FHB #82 p. 59.) After draining the heater, remove the drain cock and shine a penlight into the tank bottom and check for scale and sediment. You might find that the drain opening has sealed over with scale. Punch through the scale buildup with a screwdriver or an awl, then stick a high-pressure hose in the opening and rinse the water heater.
You mention that the hot-water outlet has two air-bubble removers, or air separators. An older, centrifugal well pump can mix a lot of air into the water it delivers to a water heater. When the heater is operated at near temperature capacity, as yours is, bleed-off (opening of faucets/valves) often is accompanied by a groaning noise. Consider installing an air separator on the cold inlet supply to the water heater if there isn’t one for this purpose already.
The noise you hear could be caused by a temperature and pressure relief valve. T&P relief valves can rumble and groan when a water heater is operated near its temperature capacity.
The groaning and rumbling might also be coming from your metering valve. If you have check valves working in conjunction with the metering valve, and they happen to be spring and ball seat, you may be getting some noise out of them. If these are defective, replace them with check valves that have a little higher psi rating.
