thermostat on water heater keeps calling for heat

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stoveliker

Minister of Fire
Nov 17, 2019
1,924
Long Island NY
I have a Vaughn S50TPPR water heater that runs off of my oil boiler that also heats my house (well, it doesn't anymore, see this site, but still...).

As of yesterday it keeps calling for heat. I.e. the light is blinking and the pump in this circuit is continuously running.

The thermostat of course does not have any identifying writing on its cap (outside or in). I took a pic with the cap off.
Even when setting the temp to its lowest setting (110 I believe), it keeps calling.

So, I think I may need a new thermometer or whole thermostat.

Can anyone tell me what thermostat this is, whether I can replace it myself, what part number I need?

IMG_20210922_123134172.jpg
 

stoveliker

Minister of Fire
Nov 17, 2019
1,924
Long Island NY
Or, how to switch the circuit off for now so I don't wear out my pump? It seems I can only switch off all at once (meaning the boiler would cool down, which I'm told risks cracking the cast iron body...)?
 

EbS-P

Minister of Fire
Jan 19, 2019
1,467
SE North Carolina
Or, how to switch the circuit off for now so I don't wear out my pump? It seems I can only switch off all at once (meaning the boiler would cool down, which I'm told risks cracking the cast iron body...
Looks like yellow and blue wires are controlling the pump. Not know much of anything, disconnecting them should turn pump off. But again. What do I really know. I would check for voltage to ground (white wire lug) to isolate the issue to the t stat. (Don’t know if circulation pump has any relays).

my in-laws always turn off the emergency boiler switch in the summer when leaving the bourse for more than 3 hours. They never had had a problem. But I can see why cold starts my not be the best.
 

stoveliker

Minister of Fire
Nov 17, 2019
1,924
Long Island NY
Voltages appear correct (24 V). Disconnecting wires will be tried - obvious last resort until fix is in.

Thanks
 

peakbagger

Minister of Fire
Jul 11, 2008
6,597
Northern NH
I dont recognize the brand but it looks like a standard thermal switch with an onboard switching relay for the pump (the black cube). The hot wire and neutral feed the relay and there is sensing bulb that goes in the brass thermowell at the bottom. If you disconnect the Hot wire (labeled on right side) that should switch off the pump. Sensing bulb switches rarely die so my guess is your relay is cooked and it failed in the on position.

My guess is when the tank is below a high setpoint the sensing bulb snaps a internal switch closed which then pulls the relay contact closed so that the pump runs. When the bulb goes over setpoint the sensing bulb opens a switch and the relay opens turning off the pump. You will need to check the voltage on the hot, the could be 24V or 120V. The Honeywell capillary bulb type switches do have some reasonable contact amperage rating. Check the amperage reading on the pump nameplate and you may be able to dispense with the relay. Alternatively put in modern ECM pump on the circulator, those new style pumps draw very few watts and the switch may be able to switch it without a relay. The problem is most pumps are 120VAC while you measured 24V so unless the pump is 24VDC there has to be 120V somewhere on the board to switch it.

I did not go comparison shopping but something like this for the switch https://www.grainger.com/product/5T...EVBrV0wfTtf7pbxZlD8aAgcqEALw_wcB&gclsrc=aw.ds
 

stoveliker

Minister of Fire
Nov 17, 2019
1,924
Long Island NY
There is a 24 V relay switch box on the side of the boiler from which the pumps are switched. The pumps do run on 120 V.

I think I'll be able to figure out what is wrong using your description. Thank you!
 

Don2222

Minister of Fire
Feb 1, 2010
8,821
Salem NH
Call the manufacturer of your water tank and they will know the part # and manufacturer of your aquastat. :)
 

stoveliker

Minister of Fire
Nov 17, 2019
1,924
Long Island NY
It is my experience that many of those mfg's want you to talk to a plumber rather than giving useful info. Hence I tried here first :)
 

Don2222

Minister of Fire
Feb 1, 2010
8,821
Salem NH
It is my experience that many of those mfg's want you to talk to a plumber rather than giving useful info. Hence I tried here first :)
I called the manufacturer of my indirect DHW tank called a SuperStor made by HTP and their technician support was very happy to give me the Manufacturer and Part # of my Honeywell aquastat L4080B-1352. :)
 
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