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Question DetailsAsked on 9/21/2017

Water heater pilot will stay on 15 min. Have to wait 2 hrs before lighting again. Changed thermocouple.

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1 Answer


I am guessing maybe the water heater is kicking on and firing during that 15 minutes, though I suppose the pilot along could do this - heating up the firebox area enough that an overtemp or flame rollout sensor is kicking the system off, then automaticlaly resetting as it cools off and automatically resets, allowing the pilot to be relit at that time. This is most likely cause I would suspect.

Some newer water heaters also have oxygen/airflow sensors detecting if there is enough air getting into the firebox and if not shut off the unit till it resets - in that case a blocked airflow filter/screen, which (now is commonly idiotically on the bottom of the heater where it cannot be seen nor reasonably cleaned, can cut down the airflow enough to trigger the sensor.

Another possible cause, though not if the main burner is firing properly, would be low gas pressure to the unit - would have to be pretty low to do this.

Other causes of pilot failure include flue drafting blowing it out, or the thermocouple not being properly in the pilot flame so it does not stay consistently properly hot. But in both those cases should relight immediately, not require 2 hours to be able to relight it.

One other cause which has possibly been the cause of several previous comments here, and my go-to plumber mentioned to me as a new issue causing unusual number of callbacks, is that a lot of cheap chinese thermocouples are coming in defective (though usually just totally failing, but might do this is the thermocouple wiring is cutting out as it heats up, then remakes contact as it cools) so it may be the replacement was defective. If a cheap brand I would try a Honeywell thermocouple (for maybe $10-30 depending on model) before going on further - if that is not the cause then you just have a spare one on hand for next changout in a few years.

Here are a few previous similar questions with answers which might also help:

If this did not help, then a Heating and A/C or Plumbing contractor (your Search the List category) is your answer to get this diagnosed.

Answered 3 years ago by LCD

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