Gas Gadget done gone?

[Doyle Phillips]

For about 3 days my water heater/boiler (old style) has been set at Tibio.
This morning it decided to turn up the heat to the very highest setting. The dial remained
at Tibio.

Have you had such a problem? Advice please. Maybe you know a repairman? Thanks.

[Mikel1]

Doyle, most likely thermostat has gone bad, but could also be the gas valve. You could probably search for both parts online if you know make and model # and determine cost effectiveness of repair vs. replacement. It would depend on how old the heater is and the brand as far as parts availability / costs.

[DonJuane]

Depending on water quality, six years is about the max for a water heater in the US. So if it's old, just buy a new one. (Which sounds simple enough until you go pay for it, that is). Bound to be at least a month or two's rent. The gotcha would be to buy a new thermostat and then the near 100% failure point, a ruptured tank would happen shortly after.

[DonJuane]

Just wondering if while testing you pulled off the plastic dial to see that it hasn't disintegrated on you while sitting for years in the sun, right? If you slide the dial off and the plastic disk shatters or crumbles, just get a pair of pliers and twist slightly clockwise and see if that starts the gas again to warm up your watet above warm. Note the pliers are only necessary to rotate the brass stemmed shaft if it is clear the plastic dial is damaged.

Also I don't know from your question if you are saying "it's been warm for a long time but I'm finally tired of that and want to change it to warmer" vs "it's been getting colder and colder and I want to get it back to where it was" of which the latter would indicate a mechanical failure of the thermostat.

So for example with normal operation, you light the pilot and turn the dial to near a center position and as you start rotating the dial toward the "warm" position, you hear when you rotate it clockwise a "click" and the gas flows and the fire flames up. Then 15-20 minutes later you hear another "click" and the gas goes off. Now you walk up to the thermostat and you turn it clockwise or more toward the hot setting. Under normal operation, you should hear another "click" when you dial clockwise and the flame should blast on again. If you don't hear the click when turning it up from warm to hot (with the fire having recently shut off), then either the dial is not rotating the brass stem of the thermostat because maybe the plastic knob has disintegrated in the sun or if you pull the plastic dial off to have a look and then take some pliers and rotate the brass stem clockwise and there is no second click at this point, then the thermostat is shot.

Again a new WH would be better at this point because if the unit is old not only are you burning money on something that is going to start leaking soon anyway but you are going to have lots of calcium built up in it, it may not drain either because of this and you've likely got a lot of corrosion in and around the tank which can even cause the tank to crack when you must use a gigantic pipe wrench to break the lock-tight thread sealant that has the thermostat secured where it is screwed in the front of the tank.