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Due to a cold house I went down to investigate my forced hot water / oil burner system. I discovered that apparently when my indirect water heater was being replaced three months ago the plumber left shut a valve. This is the valve right after the house circulator. So, the furnace must have been coming on, heating up, then stopping because no water was circulating.

Could this have damaged the circulator?

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Yes, it could. It's good that some protection switch/interlock was saving you from extensive damage, so that may have saved you.

What normally happens is the pump/circulator transfers the electrical energy to rotating mechanical energy which is then absorbed into the water and life is good. However, in your case where you were dead-heading on the valve, the water couldn't dissipate the energy transferred to the water via circulation so it builds up in a thermal manner, so the pump/circulator could have burned up.

Depending on what kind of pump/circulator you have, if you run it and it sounds like there are loose parts ("marbles") during operation, then you've killed it. Otherwise, you may have shortened the life of the pump/circulator, or you got lucky and the interlock that protected you from operating in a dead-head case caught you before you damaged the pump.

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  • How can I find out more about interlocks and whether my heating system has one? I did notice that when I opened the valve, the circulator made a purring noise like it was coming on. – Tyler Durden Sep 27 '15 at 16:26
  • You should try to find the manufacturer/serial of the boiler/heating unit. Then google it. It will tell you whether or not you have a flow switch, thermocouple, etc that would save you from disaster. If you are unsure and really want to find out (and I recommend this cautiously) you can try running it very briefly (less than 30 seconds) to see if it cuts out on you when dead-headed. – N8sBug Sep 27 '15 at 16:30

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