Runaway Thermostat?

[PM5K]

Relief valve opened on my hot water heater. The water was very hot from the tap, so I turned the unit off and ran enough water through it to get cold water into it. I checked the valve to make sure it was working properly, and then tried to turn the unit back on, however it would not turn on. I reset the breaker on the thermostat and it came back on.

So it seems to me I have a runaway thermostat.

This is just a point of use Ariston 4 gallon water heater, just want to be sure before I go pick up a thermostat, because I suppose it could also be the element.

Thanks!

(Also it's just a small point of use unit so it's off until I get it fixed)

 

[Raspy]

The element only responds to the thermostat and cannot make the water heater "run away"

 

[Sponsor]

 

[WyrTwister]

The tstat only switched one of the two hots ( 240 VAC ) I saw a WH that had an element shorted to ground on the un-switched hot . Therefore , part os the element was apparently running / heating 24/7 ?

The big box stores carry a plumbers pack with upper and lower tstat and 2 elements . That might be the way to go ?

However , if yours is a 4 gallon unit , is it 120 VAC ?

God bless
Wyr

 

[DonL]

I agree that a shorted element can cause the problem.

If they short they can weld the contacts on the thermostat.

Is that unit on 120V or 240V ?


Good Luck.