Thread: Boiler Leaking
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      10-24-2019, 11:39 AM   #9
ToddBlack88
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Quote:
Originally Posted by byroncheung View Post
sorry for thread hijacking - but i do want to ask, in my setup (have a navien tankless boiler), when the boiler isn't heating, pressure is about 13-14psi. when it heat, it would goes up to the twenties, say 22-23 etc. is that amount of increase normal or i need to have a look at my expansion tank?
Does it stay at that pressure for a bit after it stops firing and the pump shuts off, before dropping back down, or does it drop as soon as the pump shuts down?

I ask because i have found most tankless setups pump into the boiler, and with the large pressure drop design of a tankless system for efficiency, the pressure spikes within the boiler. So thaTs pretty normal.

If the pressure slowly drops back down between firings, then most likely the air charge of the expansion tank is low. I like to set the air charge at about 90% of the static , at operating temperature, system pressure. So if you have a 3 story house with the boiler in the basement, you need a system pressure of about 20psi read off the boiler gauge, when the lines are all up to temperature. Set your air charge to about 18psi.

Every system is different as some may run auxiliary heat exchangers to save the boiler if there is various plastic pipes like poly b in the system, or if the boiler does both heating and domestic generation, as well as the pressure maximum design of the exchanger in the boiler.
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