Upper thermostat failed twice in 48 hours?

[ruthrj18]

Hello all,

Avid DIY’er, currently stumped. Went to take a shower Sunday night and the water was lukewarm. Circuit breaker wasn’t tripped, power is on to my water heater but it wasn’t heating. Broke out the multimeter to test everything with the power to the water heater off.

ECO not tripped. Both the upper and lower element are reading ~13 ohm. Good, both elements are 4500 watts. Lower thermostat is good, it’s reading 0 across the terminals (with upper thermostat set at both highest or lowest settings). Upper thermostat failed: Not getting a zero reading across its terminals, upper thermostat set to max with lower thermostat set to lowest. Upper thermostat does not audibly click on or off when adjusting between highest and lowest settings.

Replaced the upper thermostat and presto, everything was working. Water heater worked overnight. Fast forward 24 hours, and I’m in the exact same situation again! Water not as hot as it should be, same exact measurements as above.

I’m stumped. What would kill a brand new upper thermostat? Seems like the brand new one is shot again.

Water heater is a 50 gallon classic series, professional by Rheem. Only 2 years old. Always have the upper and lower thermostat a set to 140, and I have a thermostatic mixing valve to bring the water down to 120 before it reaches any faucets. Any suggestions you could throw my way would be greatly appreciated. I could throw another thermostat on there but I’m worried it’ll die just as quickly without replacing something else.

 

[ruthrj18]

Pic of upper thermostat. The replacement looks 100% identical to what it replaced. Bought it at Home Depot.

 

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[Phog]

Have you checked the resistance between the heater elements & ground? And the thermostat and ground?

 

[Reach4]

your troubleshooting seems correct.

 

[ruthrj18]

Might help if I throw the units in there, lol. Yes, zero ohms Reach. I went out again to measure things with the power on. I’m getting 240 volts from the breaker supplying the upper thermostat. Upper thermostat set at highest setting, lower thermostat set at lowest setting. I’m getting zero volts at the upper element.

From what I’ve found that means replace the upper thermostat.

Resistance between elements and ground is 13 ohms for both upper and lower. Resistance between ground and upper thermostat is infinite with upper thermostat highest setting, lower thermostat lowest setting. Resistance between ground and lower thermostat is zero ohms with lower thermostat at highest setting, upper thermostat at highest or lowest setting. Resistance between lower thermostat and ground is infinite with temp on lower as low as it will go (as it should be right).

Upper thermostat does not audibly click anymore. Checked water temp from the heater and it’s at 125 straight from top of the tank itself. Can’t get the water heater to do anything with the power on no matter what thermostats are set at.

 

[ruthrj18]

I might just have to suck it up and install another new one. I have no idea why the new thermostat failed already, maybe it was a bad one. Everything else looks fine!

 

[Reach4]

As a temporary workaround, you could bypass the upper thermostat, and send the power right to the lower thermostat. As a sidebar, I have repaired electric water heaters for over 65 years and have probably replaced a DOZEN thermostats, (upper or lower). They seldom go bad.

 

[Phog]

Hi ruthjr18, when you give these resistance measurements, it sounds like you're taking them with the unit powered on. (You spoke of measurements with the parts at specific operating settings). Is that correct or an I misunderstanding? To get valid resistance measurements with a multimeter, typically everything should be completely powered off. The multimeter works by sending out a voltage, and if what you're measuring has its own voltage, it can interfere with what the multimeter sees.

 

[ruthrj18]

Hi ruthjr18, when you give these resistance measurements, it sounds like you're taking them with the unit powered on. (You spoke of measurements with the parts at specific operating settings). Is that correct or an I misunderstanding? To get valid resistance measurements with a multimeter, typically everything should be completely powered off. The multimeter works by sending out a voltage, and if what you're measuring has its own voltage, it can interfere with what the multimeter sees.

Thankfully the power was off for all resistance measurements. Sorry for any confusion! I went as far as actually disconnecting the wires from the terminals on each element after checking the thermostats to ensure I was getting the correct reading on those too.

Only time I had the power on was to go through the whole system a second time and measure voltages instead of resistance.

 

[ruthrj18]

As a temporary workaround, you could bypass the upper thermostat, and send the power right to the lower thermostat.

Good idea brother! I’ll do that tomorrow if I don’t get around to getting another thermostat. This may just all be my rotten luck getting a faulty new part. It’s happened to me before on other projects, certainly won’t be the last time!

 

[Phog]

It's really suspicious that the same part failed twice in quick succession. But I don't see anything obviously wrong here. (Like reach, I'm not a pro). Hopefully someone else can give you more suggestions because I'm stumped!

 

[ruthrj18]

It's really suspicious that the same part failed twice in quick succession. But I don't see anything obviously wrong here. (Like reach, I'm not a pro). Hopefully someone else can give you more suggestions because I'm stumped!

It’s a stretch but maybe it was a power surge? We’ve had some thunderstorms rolling through over the last couple days. I just can’t think of an obvious point in time where a close lightning strike would’ve subsequently killed the thermostat. Maybe first one failed natural causes, second one lightning? Cross your fingers for me lol!!!

 

[hj]

I would never test a water heater with the power off. I have the power on so I can tell how IS acting as opposed to how it SHOULD act. If you test a live circuit with a multimeter, you usually need a new multimeter.

 

[ruthrj18]

I would never test a water heater with the power off. I have the power on so I can tell how IS acting as opposed to how it SHOULD act. If you test a live circuit with a multimeter, you usually need a new multimeter.

Why would you need a new multimeter? Forgetting to switch between ohms and volts? I’ve never broken one on a live circuit, whoop whoop!

Again, avid DIY’er. Read quite a few sources on how to troubleshoot with power on vs off, so ended up doing it both ways to get as much data as possible. Going to pickup another thermostat. Hopefully this one lasts longer than a day!

 

[ruthrj18]

It lives again! I’ll check back in if it dies. Thank you all for double checking my troubleshooting!