"sticky" gas water heater thermostat

homer12 · 01-21-2008, 06:57 PM

No answers from plumbing or HVAC so I'll try here....

I've had this long standing issue with my water heater. I have the thermostat set to heat the water to about 130 degrees, as measured just after the burner cycles off at a nearby tap. But the burner doesn't kick on again until the temp drops to about 105 degrees. No way to get a hot shower up through 3 floors of copper pipe like that in the winter! I usually have to run some water in the AM to get the water heater to kick on so I have hot water.

And when I turn the thermostat up again after a vacation I have to turn it way up the scale before the burner kicks on. It's like the spring is stiff.

New thermos are, what, about $50? Not worth it for a 13 year old water heater. So I am slowly coming around to deciding to get a new one.

I am thinking of getting a water heater with one of those new self-powered digital controllers. Are these any good? Seems like they should provide a tighter control band.

bigMikeB · 01-21-2008, 09:53 PM

A new gas valve thermostat set for a gas water heater is more like $100 or more depending on the brand. At 13 yrs old it is time for a new unit.

homer12 · 01-22-2008, 06:55 AM

So how about my other question: Are these new self powered digital gas thermostat/valves reliable? I like the idea of setting a precise temp rather than guessing if I can get it to the same setting between hot, hotter, or very hot every time I reset it from vacation.

boman47k · 01-24-2008, 11:44 PM

Mike? Gas water heaters have thermo-coupler similar to gas heaters?

AllanJ · 01-25-2008, 08:54 AM

Gas water heaters use a thermocouple, just like gas furnaces, to kill the trickle of gas to the pilot orifice if the pilot is lost for some reason or other.

The thermostat is a somewhat independent component. The thermostat may or may not work in the same way as the thermocouple, i.e. a bulb with a capillary tube operating like a long flexible mercury thermometer* and going to a pressure operated "valve handle", or a small temperature dependent voltage generating device that controls a small self contained electrical circuit.

*Also a version like a short fat thermometer at whose far end is the "valve handle" or a plunger valve for the gas.

If you are shopping for a water heater with digital temperature control, consider that some require AC power and won't give you hot water if there is a power failure. Kind of inconvenient after a big summer storm and you got all hot and sweaty cleaning up outside and now can't take a shower.

I don't believe that the digital water heaters do anything more about the hot water itself compared to the old fashioned thermostat gas valve kind. The digital models may have such features as allowing the water to cool down only during the day if no one is home, or programmable lower temperature for vacations, or remote control.

homer12 · 01-25-2008, 10:30 AM

Yes, the thermocouple is just to keep the gas valve open. The main burner on/off is controlled by the thermostat's bi-metal spring.

All the electronic controlled gas WH's I have seen use Honeywell controllers that are "self-powered" in that they operate their circuitry from the voltage supplied by the thermocouple.

I believe, but am not sure, that they do away with the bi-metal spring thermostat and use something like a RTD to provide the temperature signal. It has to be more precise than the old bi-metal type. Maybe not as reliable in the long term, though.

Kingfisher · 01-25-2008, 10:36 AM

13 years old

just get a new one, you are going to be so mad when you fix this and it starts leaking next month

homer12 · 01-25-2008, 10:43 AM

Quote:

Originally Posted by Kingfisher

13 years old

just get a new one, you are going to be so mad when you fix this and it starts leaking next month

Exactly. No way I am going to spend $75-100 and a few hours work on such an old unit.

I was mostly trying to get input on these new electronic ones from anyone who has one before I decide. In the interim I may try to blow mine down one more time to see if that improves it's performance. It's been a few years and I suppose a layer of crud could insulate the probe to some extent and might cause some issues.

homer12 · 01-25-2008, 05:36 PM

Here is one of the WHs I am considering. Upper and lower temp sensors and self-powered electronic controls. I haven't actually seen one of these in use but it seems like it could be a significant improvement in function over the old bi-metal thermostats.

http://www.sears.com/shc/s/p_10153_1...s+water+heater