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I have an old style (without a bladder) expansion tank installed on my heating system. Recently i noticed that the water pressure fluctuates a lot in the system and wonder if that maybe because the expansion tank doesn't have enough air any more.

How often does one usually need to drain expansion tank?

What are other reasons for water pressure to fluctuate a lot during the day (almost hitting the limit when the safety valve is about to trigger).

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up vote 1 down vote accepted

I do most plumbing myself, but I hired a pro to install our new boiler. He recommended a yearly flush. The problem is the dirtier the water, the less efficient it is.

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The expansion tanks may have a gasket and a valve to pressurize them (like you have on a car tire). If that's the case, the gasket inside of the tank may have failed and the entire expansion tank would need to be replaced. If the plumber was nice, it's just a screw on fitting, and an easy DIY job to unscrew and reinstall a new one (don't forget to put some dope on the threads to avoid leaks).

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