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What's the model number of your boiler? What do you mean "no water is going out"? do you mean it's not circulating?
Is boiler cold?
Ok sounds like a bad board or a bad sensor. Give me a few to pull the specs for your boiler. A phone call is an additional charge.
Do you have an ohm meter?
Sensors are thermistors. System sensor is connected to terminals 21 & 22. Inlet sensor is S2, operating sensor is S1a, limit sensor is S1b. The readings are all different and there too much info to relay here. Here are the service manualhttp://www.lochinvar.com/_linefiles/KBII-SER%20Rev%20J.pdf
thermistor ratings on page 35and the install manual
sensor connection points shown on page 80