Wednesday, July 1, 2026 New Hot Water Tank Sensor
We were using the Triangle Tube thermostat that they supply with their hot water tanks, but its hysteresis loop had been getting bigger and bigger, finally turning on at 108 °F and turning off at 145 °F. Time to get a new one! Except our plumber couldn’t because Triangle Tube is out of business. Our plumber said he’d had a number of these thermostats fail and the hot water storage tanks have dry wells, so any thermistor that’s compatable with the Lochinvar boiler will do. The boiler is really full featured and can use either a thermostat or a sensor for the domestic hot water.
For some reason, the boiler was seeing a water temperature that was about 10 °F too high. We told the plumber not to worry about it, a nice solid, non-drifting offset can easily be dealt with. Martin put one of the Thermoworks recording thermometer sensors into the dry well of the west (second) tank and above is 4 days worth of data.
The boiler is turning on at about 128 °F and off at about 136 °F with its set temperature at 146 °F, so everything is working fine! We have the circulating hot water pump turning off at 11 PM and on at 5 AM. When it turns on you can see some wild short excursions because overnight the tanks stratify and the stirring up is chaotic, bringing hot water from the top, really hot water from the heat exchanger, if the boiler happens to be on at start up, or cold water from the bottom, or even really cold water from the recirculating return to where the sensor is.
It’s really nice being able to set the temp from the boiler control panel digitally, instead of fiddling with an analog thermostat.