I normall only turn on one central heating at a time upstairs or downstairs but when accidentally both are on, the minute that happens my water heater pilot goes off. This is proven fact.

I can only think not enough gas as they are all using gas but I have no idea, that was wild guess.

Any idea to this madness? I have searched for any related issues and I have not able to find yet.

If you know solution please share, thanks

  • 1
    What size is the gas lines that connect the furnaces,the water heater, and the main incoming line. Post a picture or an explanation of the sizes and configuration so we can get a better idea of what is happening. – d.george Feb 22 '17 at 10:16
  • I think there may be an adjustment on the WH so that you can increase the flow of gas for the pilot. Question: If the burner on the WH is on (you just made a large demand for hot water) and one furnace is on, and the other furnace burner is called, will all three come on and stay on? – Jim Stewart Feb 22 '17 at 11:31

The only way to tell for sure would be to measure the gas pressure at the water heater when both furnaces are on. This will require a gauge and probably a little plumbing. The other possibly might be a venting or combustion air issue especially if they are all in the same room or are commonly vented.

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