crown megastor temperature sensor thermistor vs. aquastat

bmwpowere36m3

I picked up a Crown mega-stor tank to use with a Lochinvar WH55 boiler. Lochinvar sells a temp sensor/thermistor with their indirects that couples with the boiler controls. The mega-stor comes with an aquastat.... and while I can wire the aquastat to the boiler, I'd prefer to use a thermistor (utilize boiler controls).

The tank's immersion well is welded and appears to be for a 3/8" bulb. The Lochinvar DHW thermistor is 1/4" and incorporates a high-temp limit (2 wires) and a tech said its a 10k NTC sensor.

I see Honeywell sells a couple 3/8" thermistors, a single element 10k NTC (2-wire) and a dual element, limit temperature
sensing function, 10k NTC (3-wire). Anyone utilize thermistors with their mega-stors?

davearcaro

I'd be interested in this subject as well.

ratio

"10k" isn't enough to get the right thermistor (although it'll get you working in a pinch). The two major flavors are Type 2 and Type 3, also known as CP and AN. 10k is the resistance of the sensor at 77° F (that's 25° socialist), so at 77° they'll read the same, but the further you get from that the more they diverge.

Check out https://www.workaci.com/products/temperature for thermistors. I can't imagine they'll be more expensive than Honeywell.

yellowdog

Use the Lochinvar sensor and shim it to fill the well. Buderus sensors have been like that for years.

hot_rod

Many of those sensors are 6 mm about .236. They fit nicely inside a piece of 5/16" soft copper tube. Which gives you 3/8" OD and slips into the 3/8" well. Use some heat transfer grease.

If it is a 1/2" ID well, a two step with 5/16 and 3/8 copper tube.

Some Honeywell sensor wells came with a tapered, curved shim as @yellowdog mentioned. Just cut a piece of copper tube with a tin snip to make a wedge to slip in with the sensor.

There is some thermal lag, but you can put the sensor against the outside of the tank also. Push it between the foam insulation and the metal tank.

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