Thoughts on how to mount a Thermocouple

Supplies & Equipment
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I had a potentially serious near miss incident the other day. The wire from the thermostat broke and i didn’t notice, starting cleaning and pretty quickly i noticed the water was extremely hot, let go of the trigger and saw the burner still going and ran over and hit the E-Stop. Had i kept going an o-ring or something would have failed and could have burned me or someone walking by. I’m adding a safety interlock that will monitor the temperature out of the burner and if it his X degrees, it’ll kill the burner.

I’m adding this meter linked below paired with a bolt on ring style thermocouple. The part i need help on is how to bolt of the thermocouple to get a relatively accurate reading. Ideally i would like a block, similar to an unloader that has 3/8 or 1/4 female threads so i can bolt on the thermocouple. Or option B, which im not as wild about is using high temp JB weld or epoxy and sticking it onto the stainless cross coming out of the heater.

Does anyone know of a high pressure block that may fit what i need?

https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-_measurement/digital_panel_meters/1-z-8_din_size/dpm2l-at-2r-hl

https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-_measurement/temperature_sensors_-a-_transmitters/rtd_(pt100)_sensors/sensors_(bolt-on_ring)/rtd1-b02l06-01

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That thermocouple looks like a surface mount for external temperatures of a structure. Have you looked at something like this?

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Ok, i think a probe type will be better suited. What size are those threads? I’d prefer 1/2" and it says high pressure but what is that actual rating?

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I’m not sure, I can’t seem to find a data sheet, you might need to call them. Best I can find is the price is either 1/4" long or 1/2" long, and it’s using 1/4" NPT threads. If you gave them a call they might even have a better recommendation.

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The other thing you could do is use a surface mount thermocouple, and use an IR gun to find out what the temperature is of your unloader body when everything is functioning correctly, then set your cutoff 10 degrees above that. Might have to change your settings a couple times to get it dialed in, but it has the benefit of no plumbing required.

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@mwpws I’m a bit confused by how that’s supposed to work, can you walk me through it a little please? Thermocouples generate a small amount of electricity when they are heated. That electricity is used to keep a gas valve open, so for instance if a pilot light goes out, the thermocouple cools down, electricity goes away, and the gas valve closes.

Are you planning on using it in reverse, so that when the thermocouple heats up the tiny amount of electricity turns something off instead?

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the thermocouple will feed into the meter. When the temperature hits a preset temp an internal relay in the meter will output 12v which will flip another relay to cut the signal to the burner

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Even with a broken thermostat your burner should’ve shut off as long as you have a flow sensor or pressure switch that is working correctly. All hot water machines usually have at least one of those or some even have both. I would check into that before adding a thermocouople.

What kind of washer is it?

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It’sa Pressure pro and yeah you’re right it should have shut off when I came off the trigger. It all happened fast so I may not have it right because the pressure switch hasn’t had problems before or after this incident.

I would feel safer with a high temp shut off anyway. I’m going to try and find a probe style thermocouple.

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Thanks! That’s the part I was missing. I didn’t realize a thermocouple’s output was precise enough to be metered like that over such a small temp spread