my OEM 2005 isotherm hot water heater malfunctioned. the tank was filled with h 2 0 and the hwh ac power switch turned on. the overheat thermostat was defective, so the AC power was not shut off when the tank started to overheat. the stainless steel tank heated up so much it warped the stainless cover plate . with a warped plate, the tank was shot. isotemp tech support confirmed that the 'old' design of overheat thermostat did not cut off AC power if tank overheat temperature was sensed, or if the overheat thermostat itself was defective. the new design of thermostat does. if you have the 'old' overheat thermostat , save yourself a $700 new tank and install bill by installing the upgraded overheat thermostat. i wish i could post a picture of the warped steel cover plate: it's quite spectacular...
isotemp hot water heater design flaw..
- Thread starter MitchM
- Start date
i asked the same question of the isotemp 'tech rep.' the 1st tech rep was unable to tell me why the tank overheated so badly it warped the cover plate. he was also unable to tell me why the pressure relief valve did not function to blow off enough water to save the tank cover. he went to ask a more senior rep who then advised of the design defect in the previous design of the overheat thermostat, which when it fails does NOT cut off AC power .. so the heating element just continues to fry itself. let's assume there is some small amount of air in the tank, and that the air and water in the tank obey's boyle's law law of gases, PV = n r T. as the water temp in the tank goes up, due to the malfunctioning 'overheat ' thermostat allowing the heating element to get red hot, the pressure inside the tank increases in direct proportion. but why that increase in pressure would not blow h 2 o out of the pressure relief valve , instead of heating the tank so much that it warps the cover plate is a mystery which no tech rep at isotemp can yet answer. i'll see if i can post pictures .
So you have a 13 year old temp/pressure relief valve? That is old. This ain't rocket science. Some particular temp control fails to do its job, your tank overheats and the water reaches the temperature/pressure relief valve blow-off threshold - pop, the tank empties and the heating element cooks itself, shorts and trips the breaker. Anything short of that risks an exploding water heater. Ask the manufacturer why they think the safety valve didn't trigger.
I don't get it, these are supposed to be high quality water heaters. But water heater relief valves are both temperature and pressure limited so whether pressure or over temp the tank should have emptied and stayed empty while the heating source turned it into an oven. Indel Webasto really needs to fully explain what happened if they want me to consider their product.
Stu Jackson once suggested that the water heater AC power supply be turned off when the water heater reaches temp. I pondered that for a few months and adopted his advice. My water heater stays turned off until we need it.
Stu Jackson once suggested that the water heater AC power supply be turned off when the water heater reaches temp. I pondered that for a few months and adopted his advice. My water heater stays turned off until we need it.
on the control of the AC WH heating element. I have been given a brain and most of the time to know when to turn something on or off. Would seem wasteful not to use it. And a
on the following of Stu's advice... More often then not it is insightful.
FYI: the hot water heater was OEM 2005. pressure relief valve is low near tank bottom manufacturer owner instructions were followed to the letter-- ie., water pump was functioning properly to fill tank with water from full water tanks. overheat thermostat failure NEW design shuts off all AC to the h w h. HWH's 'old ' 2005 design does not shut off AC if overheat thermostat fails. NOTE that both new design and old design have both a 'temperature regulating thermostat'- which stops AC to the heater element when the desired h 2 0 temp is attained , and the 'overheat' thermostat. here's the 'tech rep's latest explanation : " ...we see an increasing amount of defects when individuals ‘wet winterize’ their tanks. The tech mentioned that this antifreeze wears away at the rubber components and I believe that is exactly what has taken place. I have also seen individuals winterize their units in this exact same way and have their units bulge out from the expanding liquid and then leak from these same areas once the unit has been drained of the antifreeze and filled with water and out under pressure. I would recommend flushing the unit with antifreeze and then storing the unit dry..."my reply: NOTE that NO part of the owners manual tells you not to "winterize wet. " my old Raritan, made in NJ was winterized 'wet' with pure -50 antifreeze for 37 years- from 1980 til i sold that boat.. BUYER BEWARE: i am now on my 2nd isotemp , and it will be my last.